Timed Text Markup Language 1 (TTML1) (Third Edition)

3.2.1 Generic Processor Conformance

A TTML Content Processor conforms to this specification if the following generic processor criteria are satisfied:

1. The processor provides at least one mechanism for notionally instantiating a Reduced XML Infoset representation of a conformant Document Instance.

2. If a process does or can perform validation of a candidate Document Instance, then it provides at least one mechanism to implicitly or explicitly associate the Reduced XML Infoset representation of a conformant Document Instance with one of the Abstract Document Types defined by 4 Document Types.

3. The processor does not a priori reject or abort the processing of a conformant Document Instance unless the processor does not support some required (mandatory) feature specified or implied by a TTML profile declared to apply to the Document Instance.

4. The processor supports all mandatory processing semantics defined by this specification.

   Note:

   The phrase mandatory semantics refers to all explicit use of the conformance key phrases must and must not as well as any declarative statement that can be reasonably inferred from such key phrases. For example, these mandatory semantics include support for all features marked as mandatory in D.2 Feature Support.

5. If the processor supports some optional processing semantics defined by this specification, then it does so in a manner consistent with the defined semantics.

   Note:

   The phrase optional semantics refers to all explicit use of the conformance key phrases should, should not, may, and may not, as well as any declarative statement that can be reasonably inferred from such key phrases. For example, these optional semantics include support for all features marked as optional in D.2 Feature Support.

3.2.2 Transformation Processor Conformance

A TTML Content Processor is a conformant TTML Transformation Processor if the following criteria are satisfied:

1. The processor satisfies all requirements specified by 3.2.1 Generic Processor Conformance.

2. The processor supports the DFXP Transformation profile as specified by F.1 DFXP Transformation Profile.

3.2.3 Presentation Processor Conformance

A TTML Content Processor is a conformant TTML Presentation Processor if the following criteria are satisfied:

1. The processor satisfies all requirements specified by 3.2.1 Generic Processor Conformance.

2. The processor supports the DFXP Presentation profile as specified by F.2 DFXP Presentation Profile.

5.3.1 Core Catalog

The core vocabulary catalog is intended to satisfy the needs of TTML while providing a baseline vocabulary for future profiles. This vocabulary is divided into distinct categories, specified in detail in the following sections:

• 6 Parameters

• 7 Content

• 8 Styling

• 9 Layout

• 10 Timing

• 11 Animation

• 12 Metadata

The core element vocabulary specified for use with a Document Instance is enumerated in Table 3 – Element Vocabulary.

Element vocabulary groups that are used in defining content models for TTML element types are enumerated in Table 4 – Element Vocabulary Groups.

The attribute vocabulary specified for use with the core vocabulary catalog is enumerated in Table 5 – Attribute Vocabulary.

5.3.2 Extension Catalog

The extension vocabulary catalog is intended for use by future profiles of TTML, and is not further defined by this version of this specification.

In addition to standardized extension vocabulary, a conforming Document Instance may contain arbitrary namespace qualified elements that reside in any namespace other than those namespaces defined for use with this specification. Furthermore, a conforming Document Instance may contain arbitrary namespace qualified attributes on TTML defined vocabulary where such attributes reside in any namespace other than those defined for use with this specification.

6.1.1 ttp:profile

The ttp:profile element is used to specify a collection of used (mandatory and enabled), required (mandatory), and optional (voluntary) features and extensions that must or may be supported by a Content Processor in order to process a Document Instance that makes (or may make) use of such features and extensions.

This specification defines two distinct uses of the ttp:profile element:

• as a child of the head element within a TTML Document Instance;

• as the root element of a TTML Profile Definition Document instance;

When a ttp:profile element appears within a TTML Document Instance, its purpose is to express authorial intentions about which features and extensions must or may be supported by a recipient content processor. In addition, the element indirectly expresses information about the set of features or extensions that are (or may expected to be) used by the Document Instance.

When a ttp:profile element is used by a TTML Profile Definition Document instance, it serves to publish a machine readable specification of a specific TTML profile, of which this specification defines three such Profile Definition Documents in F Profiles.

The ttp:profile element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more ttp:features elements, followed by zero or more ttp:extensions elements.

<ttp:profile
  use = string
  xml:id = ID
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, ttp:features*, ttp:extensions*
</ttp:profile>

If specified, the use attribute must adhere to the xsd:anyURI data type defined by [XML Schema Part 2], §3.2.17, and, furthermore, must denote a profile designator in accordance with 5.2 Profiles. In this case, the profile designator must refer to (1) a standard, predefined Profile Definition Document as defined by F Profiles, or (2) a feasibly dereferenceable resource representing a valid Profile Definition Document instance. In either case, the referenced profile serves as the baseline profile of the specifying ttp:profile element.

If the use attribute is not specified, then the baseline profile of the ttp:profile element must be considered to be the empty (null) profile, i.e., a profile definition containing no feature or extension specifications.

The collection of features and extensions of a profile are determined according to the following ordered rules:

1. initialize the features and extensions of the profile to the empty set;

2. if a use attribute is present, then augment the profile with the set of features and extensions specified by the referenced baseline profile;

3. for each ttp:feature and ttp:extension element descendant of the ttp:profile element, using a post-order traversal, merge the specified feature or extension with the features and extensions of the profile, where merging a feature or extension entails replacing an existing feature or extension specification, if it already exists, or adding a new feature or extension specification, if it does not yet exist in the profile;

A conformant TTML processor is not required to be able to dereference a Profile Definition Document that is not one of the standard, predefined profiles defined by F Profiles. Furthermore, a conformant TTML processor may make use of a built-in, static form of each standard, predefined profile so as not to require dereferencing a network resource.

If a TTML processor is unable to dereference a non-standard Profile Definition Document, then it must not further process the document without the presence of an explicit override from an end-user or some implementation specific parameter traceable to an end-user or to a user or system configuration setting. If a TTML processor aborts processing of a Document Instance due to the inability to reference a non-standard Profile Definition Document, then some end-user notification should be given unless the end-user or system has disabled such a notification, or if the processor does not permit or entail the intervention of an end-user.

The ttp:profile element is illustrated by the following example.

<ttp:profile use="dfxp-presentation">
  <ttp:features xml:base="http://www.w3.org/ns/ttml/feature/">
    <ttp:feature>#text-outline</ttp:feature>
  </ttp:features>
</ttp:profile>

6.1.2 ttp:features

The ttp:features element is a container element used to group infomation about feature support requirements.

The ttp:features element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more ttp:feature elements.

<ttp:features
  xml:base = string : TT Feature Namespace
  xml:id = ID
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, ttp:feature*
</ttp:features>

If specified, the xml:base attribute must (1) adhere to the xsd:anyURI data type defined by [XML Schema Part 2], §3.2.17, (2) express an absolute URI that adheres to [XML Base] and, (3) express a feature namespace as defined by D.1 Feature Designations. If not specified, the xml:base attribute's default value applies, which is the TT Feature Namespace.

The xml:base attribute is used to permit the abbreviation of feature designation URIs expressed by child ttp:feature elements.

6.1.3 ttp:feature

The ttp:feature element is used to specify infomation about support requirements for a particular feature.

The children of the ttp:feature element must express a non-empty sequence of character information items that adheres to the xsd:anyURI data type defined by [XML Schema Part 2], §3.2.17.

<ttp:feature
  value = (optional|required|use) : required
  xml:id = ID
  {any attribute not in default or any TT namespace}>
  Content: #PCDATA
</ttp:feature>

If the URI expressed by the content of the ttp:feature element is a relative URI, then, when combined with the feature namespace value expressed by the xml:base attribute of the nearest ancestor ttp:features element, it must express an absolute URI. In either case (original absolute URI or resulting absolutized URI), the URI expressed by the ttp:feature element must further adhere to the syntax of a feature designation as defined by D.1 Feature Designations, and, furthermore, the specific designation that appears in this URI, i.e., the portion of the feature designation that starts with the fragment identifier separator '#', must be defined by this specification or some published version thereof (that has achieved REC status).

If the URI expressed by the content of the ttp:feature element is a relative URI, then an xml:base attribute should be specified on the nearest ancestor ttp:features element.

The value attribute specifies whether a conforming TTML processor must or may implement the designated feature in order to process the document. If the value of the value attribute is optional, then the processor need not implement or otherwise support the feature in order to process the document; if the value is required, then the processor must implement or otherwise support the feature, irrespective of whether the feature is enabled or disabled, in order to process the document; if the value is use, then the processor must both (1) implement or otherwise support the feature and (2) have enabled (activated) use of the feature.

If the value of the value attribute is required or use and the TTML processor implementation does not support the feature, or if the value attribute is use and the TTML processor implementation supports but has disabled that feature, then it must not further process the document without the presence of an explicit override from an end-user or some implementation specific parameter traceable to an end-user or to a user or system configuration setting. If a TTML processor aborts processing of a Document Instance due to the specification of a required, but unsupported feature by this element, then some end-user notification should be given unless the end-user or system has disabled such a notification, or if the processor does not permit or entail the intervention of an end-user.

If the value of the value attribute is optional, and if the TTML processor implementation does not support the feature, then it may further process the document even in the case that some use of the feature is present in the document. In the case of actual use of a feature designated as optional, the default semantics associated with that feature apply; that is, the processor may behave as if the feature were not actually used or referenced by the document. Notwithstanding the above, the syntactic presence or reference to an optional feature by a document must not be considered to be a violation of document validity or a barrier to further processing if the syntactic expression is well-formed and valid.

If some defined (i.e., standardized) or otherwise well known feature is not specified by a ttp:feature element in a given profile, then it must be interpreted as if the feature were specified with the value attribute equal to optional.

The ttp:feature element is illustrated by the following example.

<ttp:profile use="http://www.w3.org/ns/ttml/profile/dfxp-presentation">
  <ttp:features xml:base="http://www.w3.org/ns/ttml/feature/">
    <ttp:feature value="required">#fontStyle-italic</ttp:feature>
    <ttp:feature value="required">#textDecoration-under</ttp:feature>
  </ttp:features>
</ttp:profile>

6.1.4 ttp:extensions

The ttp:extensions element is a container element used to group infomation about extension support requirements.

The ttp:extensions element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more ttp:extension elements.

<ttp:extensions
  xml:base = string : TT Extension Namespace
  xml:id = ID
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, ttp:extension*
</ttp:extensions>

If specified, the xml:base attribute must (1) adhere to the xsd:anyURI data type defined by [XML Schema Part 2], §3.2.17, (2) express an absolute URI that adheres to [XML Base] and, (3) express an extension namespace as defined by E.1 Extension Designations. If not specified, the xml:base attribute's default value applies, which is the TT Extension Namespace.

The xml:base attribute is used to permit the abbreviation of feature designation URIs expressed by child ttp:extension elements.

6.1.5 ttp:extension

The ttp:extension element is used to specify infomation about support requirements for a particular extension.

The children of the ttp:extension element must express a non-empty sequence of character information items that adheres to the xsd:anyURI data type defined by [XML Schema Part 2], §3.2.17.

<ttp:extension
  value = (optional|required|use) : required
  xml:id = ID
  {any attribute not in default or any TT namespace}>
  Content: #PCDATA
</ttp:extension>

If the URI expressed by the content of the ttp:extension element is a relative URI, then, when combined with the extension namespace value expressed by the xml:base attribute of the nearest ancestor ttp:extensions element, it must express an absolute URI. In either case (original absolute URI or resulting absolutized URI), the URI expressed by the ttp:extension element must further adhere to the syntax of an extension designation as defined by E.1 Extension Designations.

If the URI expressed by the content of the ttp:extension element is a relative URI, then an xml:base attribute should be specified on the nearest ancestor ttp:extensions element.

The value attribute specifies whether a conforming TTML processor must or may implement the designated extension in order to process the document. If the value of the value attribute is optional, then the processor need not implement or otherwise support the extension in order to process the document; if the value is required, then the processor must implement or otherwise support the extension in order to process the document; if the value is use, then the processor must both (1) implement or otherwise support the extension and (2) enable (activate) use of the extension.

If the value of the value attribute is required or use and the TTML processor implementation does not support the extension, or if the value attribute is use and the TTML processor implementation supports but has disabled that extension, then it must not further process the document without the presence of an explicit override from an end-user or some implementation specific parameter traceable to an end-user or to a user or system configuration setting. If a TTML processor aborts processing of a Document Instance due to the specification of a required, but unsupported extension by this element, then some end-user notification should be given unless the end-user or system has disabled such a notification, or if the processor does not permit or entail the intervention of an end-user.

If the value of the value attribute is optional, and if the TTML processor implementation does not support the extension, then it may further process the document even in the case that some use of the extension is present in the document. In the case of actual use of an extension designated as optional, the default semantics associated with that extension apply; that is, the processor may behave as if the extension were not actually used or referenced by the document. Notwithstanding the above, the syntactic presence or reference to an optional extension by a document must not be considered to be a violation of document validity or a barrier to further processing if the syntactic expression is well-formed and valid.

If some well known extension is not specified by a ttp:extension element in a given profile, then it must be interpreted as if the extension were specified with the value attribute equal to optional.

The ttp:extension element is illustrated by the following example.

<ttp:profile use="http://www.w3.org/ns/ttml/profile/dfxp-transformation">
  <ttp:extensions xml:base="http://example.org/ttml/extension/">
    <ttp:extension value="use">#prefilter-by-language</ttp:extension>
  </ttp:extensions>
</ttp:profile>

6.2.1 ttp:cellResolution

The ttp:cellResolution attribute may be used by an author to express the number of horizontal and vertical cells into which the Root Container Region area is divided for the purpose of expressing presentation semantics in terms of a uniform grid.

If specified, the value of this attribute must adhere to the following syntax:

ttp:cellResolution
  : columns rows                            // columns != 0; rows != 0

columns | rows
  : <digit>+

If not specified, the number of columns and rows must be considered to be 32 and 15, respectively. If specified, then columns or rows must not be zero (0).

A ttp:cellResolution attribute is considered to be significant only when specified on the tt element.

Except where indicated otherwise, when a <length> expressed in cells denotes a dimension parallel to the inline or block progression dimension, the cell's dimension in the inline or block progression dimension applies, respectively.

6.2.2 ttp:clockMode

The ttp:clockMode attribute is used to specify the interpretation of time expressions as real-time time coordinates when operating with time base of clock as defined by 6.2.11 ttp:timeBase.

If specified, the value of this attribute must adhere to the following syntax:

ttp:clockMode
  : "local"
  | "gps"
  | "utc"

If the time base, defined by 6.2.11 ttp:timeBase, is designated as clock, then this parameter applies as follows: if the parameter's value is local, then time expressions are interpreted as local wall-clock time coordinates; if utc, then time expressions are interpreted as UTC time coordinates [UTC]; if gps, then time expressions are interpreted as GPS time coordinates [GPS].

If not specified, the value of this parameter must be considered to be utc.

A ttp:clockMode attribute is considered to be significant only when specified on the tt element.

6.2.3 ttp:dropMode

The ttp:dropMode attribute is used to specify constraints on the interpretation and use of frame counts that correspond with [SMPTE 12M] time coordinates when operating with time base of smpte as defined by 6.2.11 ttp:timeBase.

If specified, the value of this attribute must adhere to the following syntax:

ttp:dropMode
  : "dropNTSC"
  | "dropPAL"
  | "nonDrop"

If the time base, defined by 6.2.11 ttp:timeBase, is designated as smpte, then this parameter applies as follows: if the parameter's value is nonDrop, then, within any given second of a time expression, frames count from 0 to N−1, where N is the value specified by the ttp:frameRate parameter, but while ignoring any value specified by the ttp:frameRateMultiplier parameter.

If this parameter's value is dropNTSC, then, within any given second of a time expression except the second 00, frames count from 0 to N−1, where N is the value specified by the ttp:frameRate parameter, but while ignoring any value specified by the ttp:frameRateMultiplier parameter. If the second of a time expression is 00 and the minute of the time expression is not 00, 10, 20, 30, 40, or 50, then frame codes 00 and 01 are dropped during that second; otherwise, these frame codes are not dropped.

If this parameter's value is dropPAL, then, within any given second of a time expression except the second 00, frames count from 0 to N−1, where N is the value specified by the ttp:frameRate parameter, but while ignoring any value specified by the ttp:frameRateMultiplier parameter. If the second of a time expression is 00 and the minute of the time expression is even but not 00, 20, or 40, then frame codes 00 through 03 are dropped during that second; otherwise, these frame codes are not dropped.

If not specified, then nonDrop must be assumed to apply.

A ttp:dropMode attribute is considered to be significant only when specified on the tt element.

6.2.4 ttp:frameRate

The ttp:frameRate attribute is used to specify the frame rate of a related media object or the intrinsic frame rate of a Document Instance in case it is intended to function as an independent media object.

If specified, the value of this attribute must adhere to the following syntax:

ttp:frameRate
  : <digit>+                                // value > 0

The frame rate that applies to a Document Instance is used to interpret time expressions that are expressed in frames as defined by 10.3.1 <timeExpression>.

If the media time base applies and the effective frame rate is integral, then a frame is interpreted as a division of a second of media time, such that if the frame rate is specified as F, then a second of media time is divided into F intervals of equal duration, where each interval is labeled as frame f, with f ∈ [0…F−1].

If not specified, the frame rate must be considered to be equal to some application defined frame rate, or if no application defined frame rate applies, then thirty (30) frames per second. If specified, then the frame rate must be greater than zero (0).

A ttp:frameRate attribute is considered to be significant only when specified on the tt element.

6.2.5 ttp:frameRateMultiplier

The ttp:frameRateMultiplier attribute is used to specify a multiplier to be applied to the frame rate specified by a ttp:frameRate attribute in order to compute the effective frame rate.

If specified, the value of this attribute must adhere to the following syntax:

ttp:frameRateMultiplier
  : numerator denominator                   // numerator != 0; denominator != 0

numerator | denominator
  : <digit>+

A frame rate multiplier is used when the desired frame rate cannot be expressed as an integral number of frames per second.

If not specified, the frame rate multiplier must be considered to be equal to some application defined frame rate multiplier, or if no application defined frame rate multiplier applies, then one (1:1). Both numerator and denominator must be non-zero.

A ttp:frameRateMultiplier attribute is considered to be significant only when specified on the tt element.

6.2.6 ttp:markerMode

The ttp:markerMode attribute is used to specify constraints on the interpretation and use of time expressions that correspond with [SMPTE 12M] time coordinates when operating with time base of smpte as defined by 6.2.11 ttp:timeBase.

If specified, the value of this attribute must adhere to the following syntax:

ttp:markerMode
  : "continuous"
  | "discontinuous"

If the time base, defined by 6.2.11 ttp:timeBase, is designated as smpte, then this parameter applies as follows: if the parameter's value is continuous, then [SMPTE 12M] time coordinates may be assumed to be linear and either monotonically increasing or decreasing; however, if discontinuous, then any assumption must not be made regarding linearity or monotonicity of time coordinates.

If not specified, the value of this parameter must be considered to be discontinuous.

A ttp:markerMode attribute is considered to be significant only when specified on the tt element.

If a value of continuous applies, then time expressions may be converted to real time coordinates by taking into account the computed frame rate and drop mode as expressed by the ttp:dropMode parameter. In this case, the Content Processor must create and maintain a Synthetic SMPTE Document Syncbase within which these time expressions are interpreted as further described in 10.4 Time Intervals.

If a value of discontinuous applies, then time expressions must not be converted to real time coordinates, arithmetical operators (addition, multiplication) are not defined on time expressions, and, consequently, any (well-formed) expression of a duration must be considered to be invalid.

6.2.7 ttp:pixelAspectRatio

The ttp:pixelAspectRatio attribute may be used by a content author to express the aspect ratio of non-square pixels in the production of content that makes use of pixel coordinates.

If specified, the value of this attribute must adhere to the following syntax:

ttp:pixelAspectRatio
  : width height                            // width != 0; height != 0

width | height
  : <digit>+

If not specified, then square pixels (i.e., aspect ratio 1:1) must be assumed to apply. If specified, then both width and height must be non-zero.

A ttp:pixelAspectRatio attribute is considered to be significant only when specified on the tt element.

6.2.8 ttp:profile

The ttp:profile attribute may be used by a content author to express the profile of the Timed Text Markup Language (TTML) used in a Document Instance.

If specified, the value of this attribute must adhere to the xsd:anyURI data type defined by [XML Schema Part 2], §3.2.17, and, further, must specify a profile designator in accordance with 5.2 Profiles.

A ttp:profile attribute is considered to be significant only when specified on the tt element.

6.2.9 ttp:subFrameRate

The ttp:subFrameRate attribute is used to specify the sub-frame rate of a related media object or the intrinsic sub-frame rate of a Document Instance in case it is intended to function as an independent media object.

If specified, the value of this attribute must adhere to the following syntax:

ttp:subFrameRate
  : <digit>+                                // value > 0

The sub-frame rate that applies to a Document Instance is used to interpret time expressions that are expressed in sub-frames as defined by 10.3.1 <timeExpression>.

If the media time base applies and the effective frame rate is integral, a sub-frame is interpreted as a division of a frame of media time, such that if the sub-frame rate is specified as S, then a frame of media time is divided into S intervals of equal duration, where each interval is labeled as sub-frame s, with s ∈ [0…S−1].

If not specified, the sub-frame rate must be considered to be equal to some application defined sub-frame rate, or if no application defined sub-frame rate applies, then one (1). If specified, then the sub-frame rate must be greater than zero (0).

A ttp:subFrameRate attribute is considered to be significant only when specified on the tt element.

6.2.10 ttp:tickRate

The ttp:tickRate attribute is used to specify the tick rate of a related media object or the intrinsic tick rate of content of a Document Instance in case it is intended to function as an independent media object.

If specified, the value of this attribute must adhere to the following syntax:

ttp:tickRate
  : <digit>+                                // value > 0

The tick rate that applies to a Document Instance is used to interpret time expressions that are expressed in ticks by using the t metric as defined by 10.3.1 <timeExpression>.

If the media time base applies, a tick is interpreted as an integral division of a second of media time, such that if the tick rate is specified as T, then a second of media time is divided into T intervals of equal duration, where each interval is labeled as tick t, with t ∈ [0…T−1].

If not specified, then if a frame rate is specified, the tick rate must be considered to be the effective frame rate multiplied by the sub-frame rate (i.e., ticks are interpreted as sub-frames); or, if no frame rate is specified, the tick rate must be considered to be one (1) tick per second of media time. If specified, then the tick rate must not be zero (0).

A ttp:tickRate attribute is considered to be significant only when specified on the tt element.

6.2.11 ttp:timeBase

The ttp:timeBase attribute is used to specify the temporal coordinate system by means of which time expressions are interpreted in a Document Instance.

If specified, the value of this attribute must adhere to the following syntax:

ttp:timeBase
  : "media"
  | "smpte"
  | "clock"

If the time base is designated as media, then a time expression denotes a coordinate in some media object's time line, where the media object may be an external media object with which the content of a Document Instance is to be synchronized, or it may be the content of a Document Instance itself in a case where the timed text content is intended to establish an independent time line.

If the time base is designated as smpte, then a time expression denotes a [SMPTE 12M] time coordinate with which the content of a Document Instance is to be synchronized. In this case, the value of the ttp:markerMode and ttp:dropMode parameters apply, as defined by 6.2.6 ttp:markerMode and 6.2.3 ttp:dropMode, respectively.

If the time base is designated as clock, then the time expression denotes a coordinate in some real-world time line as established by some real-time clock, such as the local wall-clock time or UTC (Coordinated Universal Time) or GPS (Global Positioning System) time lines.

If not specified, the default time base must be considered to be media.

A ttp:timeBase attribute is considered to be significant only when specified on the tt element.

When operating with either media or smpte time bases, a diachronic presentation of a Document Instance may be subject to transformations of the controlling time line, such as temporal reversal, dilation (expansion), or constriction (compression); however, when operating with the clock time base, no transformations are permitted, and diachronic presentation proceeds on a linear, monotonically increasing time line based on the passage of real time.

7.1.1 tt

The tt element serves as the root document element of a Document Instance.

The tt element accepts as its children zero or one head element followed by zero or one body element.

<tt
  tts:extent = string
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve) : default
  {any attribute in TT Parameter namespace}
  {any attribute not in default or any TT namespace}>
  Content: head?, body?
</tt>

The Root Temporal Extent, i.e., the time interval over which a Document Instance is active, has an implicit duration that is equal to the implicit duration of the body element of the document, if the body element is present, or zero, if the body element is absent.

If the tts:extent attribute is specified on the tt element, then it must adhere to 8.2.7 tts:extent, in which case it specifies the spatial extent of the Root Container Region in which content regions are located and presented. If no tts:extent attribute is specified, then the spatial extent of the Root Container Region is considered to be determined by the Document Processing Context. The origin of the Root Container Region is determined by the Document Processing Context.

An xml:lang attribute must be specified on the tt element. If the attribute value is empty, it signifies that there is no default language that applies to the text contained within the Document Instance.

If no xml:space attribute is specified upon the tt element, then it must be considered as if the attribute had been specified with a value of default.

7.1.2 head

The head element is a container element used to group header matter, including metadata, profile, styling, and layout information.

The head element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more elements in the Parameters.class element group, followed by zero or one styling element, followed by zero or one layout element.

Any metadata specified by children in the Metadata.class element group applies semantically to the Document Instance as a whole, and not just the head element.

Any parameters specified by children in the Parameters.class element group applies semantically to the Document Instance as a whole, and not just the head element.

A styling child element is used to specify style constructs that are referenced from other style constructs, by layout constructs, and by Content elements.

A layout child element is used to specify layout constructs that are referenced by Content elements.

<head
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Parameters.class*, styling?, layout?
</head>

To the extent that time semantics apply to the content of the head element, the implied time interval of this element is defined to be coterminous with the Root Temporal Extent.

7.1.3 body

The body element functions as a logical container and a temporal structuring element for a sequence of textual content units represented as logical divisions.

The body element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more elements in the Animation.class element group, followed by zero or more div elements.

Any metadata specified by children in the Metadata.class element group applies semantically to the body element and its descendants as a whole.

Any animation elements specified by children in the Animation.class element group apply semantically to the body element.

<body
  begin = <timeExpression>
  dur = <timeExpression>
  end = <timeExpression>
  region = IDREF
  style = IDREFS
  timeContainer = (par|seq)
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Metadata namespace}
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Animation.class*, div*
</body>

An author may specify a temporal interval for a body element using the begin, dur, and end attributes. If the begin point of this interval remains unspecified, then the begin point is interpreted as the beginning point of the Root Temporal Extent. Similarly, if the end point of this interval remains unspecified, then the end point is interpreted as the ending point of the Root Temporal Extent.

If relative begin or end times are specified on the body element, then these times are resolved by reference to the beginning and ending time of the Root Temporal Extent.

If the Root Temporal Extent is shorter than the computed duration of the body element, then the active time interval of a body element is truncated to the active end point of the Root Temporal Extent.

An author may associate a set of style properties with a body element by means of either the style attribute or inline style attributes or a combination thereof.

If no timeContainer attribute is specified on a body element, then it must be interpreted as having parallel time containment semantics.

7.1.4 div

The div element functions as a logical container and a temporal structuring element for a sequence of textual content units represented as logical sub-divisions or paragraphs.

The div element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more elements in the Animation.class element group, followed by zero or more div or p elements.

Any metadata specified by children in the Metadata.class element group applies semantically to the div element and its descendants as a whole.

Any animation elements specified by children in the Animation.class element group apply semantically to the div element.

<div
  begin = <timeExpression>
  dur = <timeExpression>
  end = <timeExpression>
  region = IDREF
  style = IDREFS
  timeContainer = (par|seq)
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Metadata namespace}
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Animation.class*, Block.class*
</div>

An author may associate a set of style properties with a div element by means of either the style attribute or inline style attributes or a combination thereof.

If no timeContainer attribute is specified on a div element, then it must be interpreted as having parallel time containment semantics.

7.1.5 p

A p element represents a logical paragraph, serving as a transition between block level and inline level formatting semantics.

The p element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more elements in the Animation.class element group, followed by zero or more intermixed span elements, br elements, or text nodes.

Any metadata specified by children in the Metadata.class element group applies semantically to the p element and its descendants as a whole.

Any animation elements specified by children in the Animation.class element group apply semantically to the p element.

<p
  begin = <timeExpression>
  dur = <timeExpression>
  end = <timeExpression>
  region = IDREF
  style = IDREFS
  timeContainer = (par|seq)
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Metadata namespace}
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Animation.class*, Inline.class*
</p>

An author may associate a set of style properties with a p element by means of either the style attribute or inline style attributes or a combination thereof.

If no timeContainer attribute is specified on a p element, then it must be interpreted as having parallel time containment semantics.

If a sequence of children of a p element consists solely of character information items, then that sequence must be considered to be an anonymous span for the purpose of applying style properties that apply to span elements.

7.1.6 span

The span element functions as a logical container and a temporal structuring element for a sequence of textual content units having inline level formatting semantics.

When presented on a visual medium, a span element is intended to generate a sequence of inline areas, each containing one or more glyph areas.

The span element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more elements in the Animation.class element group, followed by zero or more intermixed span elements, br elements, or text nodes.

Any metadata specified by children in the Metadata.class element group applies semantically to the span element and its descendants as a whole.

Any animation elements specified by children in the Animation.class element group apply semantically to the span element.

<span
  begin = <timeExpression>
  dur = <timeExpression>
  end = <timeExpression>
  region = IDREF
  style = IDREFS
  timeContainer = (par|seq)
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Metadata namespace}
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Animation.class*, Inline.class*
</span>

An author may associate a set of style properties with a span element by means of either the style attribute or inline style attributes or a combination thereof.

If no timeContainer attribute is specified on a span element, then it must be interpreted as having parallel time containment semantics.

7.1.7 br

The br element denotes an explicit line break.

Any metadata specified by children in the Metadata.class element group applies semantically to the br element and its descendants as a whole.

Any animation elements specified by children in the Animation.class element group apply semantically to the br element.

<br
  style = IDREFS
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Metadata namespace}
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Animation.class*
</br>

When presented on a visual medium, the presence of a br element must be interpreted as a forced line break.

7.2.1 xml:id

The xml:id attribute is used as defined by [XML ID].

The xml:id attribute may be used with any element in the core vocabulary catalog.

7.2.2 xml:lang

The xml:lang attribute is used as defined by [XML 1.0], §2.12, Language Identification.

The xml:lang attribute must be specified on the tt element and may be specified by an instance of any other element type in the core vocabulary catalog except parameter vocabulary.

7.2.3 xml:space

The xml:space attribute is used as defined by [XML 1.0], §2.10, White Space Handling.

The xml:space attribute may be used with any element in the core vocabulary catalog except parameter vocabulary.

The semantics of the value default are fixed to mean that when performing presentation processing of a Document Instance as described by 9.3.4 Synchronic Flow Processing, processing must occur as if the following properties were specified on the affected elements of an equivalent intermediate XSL-FO document:

• suppress-at-line-break="auto"

• linefeed-treatment="treat-as-space"

• white-space-collapse="true"

• white-space-treatment="ignore-if-surrounding-linefeed"

Similarly, the semantics of the value preserve are fixed to mean that when performing presentation processing, processing must occur as if the following properties were specified on the affected elements of an equivalent intermediate XSL-FO document:

• suppress-at-line-break="retain"

• linefeed-treatment="preserve"

• white-space-collapse="false"

• white-space-treatment="preserve"

When performing other types of processing intended to eventually result in a visual presentation by means other than those described in this specification, the semantics of space collapsing and preservation as described above should be respected. For other types of processing, the treatment of the xml:space attribute is processor dependent, but should respect the semantics described above if possible.

8.1.1 styling

The styling element is a container element used to group styling matter, including metadata that applies to styling matter.

The styling element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more style elements.

<styling
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, style*
</styling>

To the extent that time semantics apply to the content of the styling element, the implied time interval of this element is defined to be coterminous with the Root Temporal Extent.

8.1.2 style

The style element is used to define a set of style specifications expressed as a specified style set in accordance with 8.4.4.2 Specified Style Set Processing.

<style
  style = IDREFS
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
 Content: EMPTY
</style>

If a style element appears as a descendant of a region element, then the style element must be ignored for the purpose of computing referential styles as defined by 8.4.1.2 Referential Styling and 8.4.1.3 Chained Referential Styling.

8.2.1 style

The style attribute is used by referential style association to reference one or more style elements each of which define a style (property) set.

The style attribute may be specified by an instance of the following element types:

• body

• br

• div

• p

• region

• span

• style

If specified, the value of a style attribute must adhere to the IDREFS data type defined by [XML Schema Part 2], § 3.3.10, and, furthermore, each IDREF must reference a style element which has a styling element as an ancestor.

If the same IDREF, ID₁, appears more than one time in the value of a style attribute, then there should be an intervening IDREF, ID₂, where ID₂ is not equal to ID₁.

8.2.2 tts:backgroundColor

The tts:backgroundColor attribute is used to specify a style property that defines the background color of a region or an area generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

The tts:backgroundColor style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="306px 114px"/>
  <style tts:backgroundColor="red"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:padding="3px 40px"/>
</region>
...
<p region="r1" tts:backgroundColor="purple" tts:textAlign="center">
  Twinkle, twinkle, little bat!<br/>
  How <span tts:backgroundColor="green">I wonder</span> where you're at!
</p>

Example Rendition – Background Color

8.2.3 tts:color

The tts:color attribute is used to specify a style property that defines the foreground color of marks associated with an area generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

The initial value of the tts:color property is considered to be implementation dependent. In the absence of end-user preference information, a conformant presentation processor should use an initial value that is highly contrastive to the background color of the Root Container Region.

The tts:color style is illustrated by the following example.

<region xml:id="r1">
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
</region>
...
<p region="r1">
  In spring, when woods are <span tts:color="green">getting green</span>,<br/>
  I'll try and tell you what I mean.
</p>

Example Rendition – Color

8.2.4 tts:direction

The tts:direction attribute is used to specify a style property that, depending on the context of use, determines (1) the bidirectional paragraph level, or (2) the directionality of a bidirectional embedding or override.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

When applied to a p element, the computed value of this property explicitly establishes the paragraph level as specified by [UAX9], § 4.3, Higher Level Protocol HL1.

When applied to a span element (or anonymous span), the computed value of this property, in combination with the computed value of the tts:unicodeBidi style property, determines the directionality of a bidirectional embedding or override as specified by [UAX9], § 4.3, Higher Level Protocol HL3.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value ltr.

The tts:direction style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="265px 84px"/>
  <style tts:padding="5px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
</region>
...
<p region="r1">
  Little birds are playing<br/>
  Bagpipes on the shore,<br/>
  <span tts:unicodeBidi="bidiOverride" tts:direction="rtl">where the tourists snore.</span>
</p>

Example Rendition – Direction

8.2.5 tts:display

The tts:display attribute is used to specify a style property that defines whether an element is a candidate for layout and composition in a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If the value of this attribute is auto, then the affected element is a candidate for region layout and presentation; however, if the value is none, then the affected element and its descendants must be considered ineligible for region layout and presentation.

The tts:display style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="369px 119px"
            tts:backgroundColor="black"
            tts:color="white"
            tts:displayAlign="before"
            tts:textAlign="start"/>
</region>
...
<div region="r1">
  <p dur="5s">
    [[[
    <span tts:display="none">
      <set begin="1s" dur="1s" tts:display="auto"/>
      Beautiful soup,
    </span>
    <span tts:display="none">
      <set begin="2s" dur="1s" tts:display="auto"/>
      so rich and green,
    </span>
    <span tts:display="none">
      <set begin="3s" dur="1s" tts:display="auto"/>
      waiting in a hot tureen!
    </span>
    ]]]
  </p>
</div>

Example Rendition – Display

8.2.6 tts:displayAlign

The tts:displayAlign attribute is used to specify a style property that defines the alignment of block areas in the block progression direction.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value before.

The tts:displayAlign style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="128px 66px" tts:origin="0px 0px"
       tts:backgroundColor="black" tts:color="white"/>
  <style tts:displayAlign="before"/>
  <style tts:textAlign="start"/>
</region>
<region xml:id="r2">
  <style tts:extent="192px 66px" tts:origin="128px 66px"/>
       tts:backgroundColor="green" tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="start"/>
</region>
<region xml:id="r3">
  <style tts:extent="128px 66px"/> style tts:origin="0px 132px"
       tts:backgroundColor="black" tts:color="white"/>
  <style tts:displayAlign="before"/>
  <style tts:textAlign="start"/>
</region>
<region xml:id="r4">
  <style tts:extent="192px 66px" tts:origin="128px 198px"/>
       tts:backgroundColor="green" tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="start"/>
</region>
...
<div>
  <p region="r1">I sent a message to the fish:</p>
  <p region="r2">I told them<br/> "This is what I wish."</p>
  <p region="r3">The little fishes of the sea,</p>
  <p region="r4">They sent an<br/> answer back to me.</p>
</div>

Example Rendition – Display Align

8.2.7 tts:extent

The tts:extent attribute is used to specify the width and height of a region area (which may be the Root Container Region).

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If the value of this attribute consists of two <length> specifications, then they must be interpreted as width and height, where the first specification is the width, and the second specification is the height.

The <length> value(s) used to express extent must be non-negative.

If the value of this attribute is auto, then the computed value of the style property must be considered to be the same as the extent of the Root Container Region.

The extent of the Root Container Region is determined either by a tts:extent specified on the tt element, if present, or as described by 7.1.1 tt if not present. If tts:extent is specified on the tt element, then the width and height must be expressed in terms of two <length> specifications, and these specifications must be expressed as non-percentage, definite lengths using pixel units.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the closest supported value.

The tts:extent style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="330px 122px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
</region>
...
<p region="r1">
  'Tis the voice of the Lobster:<br/>
  I heard him declare,<br/>
  "You have baked me too brown,<br/>
  I must sugar my hair."
</p>

Example Rendition – Extent

8.2.8 tts:fontFamily

The tts:fontFamily attribute is used to specify a style property that defines the font family from which glyphs are selected for glyph areas generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must attempt to map the computed font family to a supported font family that has similar typographic characteristics, or, in the absence of such a mapping, it must use the value default.

The tts:fontFamily style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="474px 146px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="center"/>
  <style tts:textAlign="start"/>
  <style tts:fontFamily="proportionalSansSerif"/>
</region>
...
<div region="r1">
  <p>
    "The time has come," the Walrus said,<br/>
    "to talk of many things:
  </p>
  <p tts:textAlign="end" tts:fontFamily="monospaceSerif">
    Of shoes, and ships, and sealing wax,<br/>
    Of cabbages and kings,
  </p>
  <p>
    And why the sea is boiling hot,<br/>
    and whether pigs have wings."
  </p>
</div>

Example Rendition – Font Family

8.2.9 tts:fontSize

The tts:fontSize attribute is used to specify a style property that defines the font size for glyphs that are selected for glyph areas generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

The computed value of the property associated with this attribute consists of a 2-tuple the entries of which denote the computed values of the width and height components of the font size respectively.

If a single <length> value is specified, then this length applies equally to horizontal and vertical size of a glyph's EM square; if two <length> values are specified, then the first expresses the horizontal size and the second expresses vertical size.

If horizontal and vertical sizes are expressed independently, then the units of the <length> values must be the same.

Relative <length> values that appear in this attribute, i.e., values expressed in percentage (%), cell (c), or EM (em) units, are resolved in relation to a referenced 2-dimensional size value consisting of two components, a width component and a height component.

When a single relative <length> value is specified, then this <length> is resolved in terms of the height component of the referenced value; when two relative <length> values are specified, the first <length> is resolved in terms of the width component of the referenced value and the second <length> is resolved in terms of the height component of the referenced value.

If the relative unit is cell (c), then the referenced value is the Computed Cell Size.

If the relative unit is EM (em), then the referenced value is determined as if percentage units were used, where 1em equals 100%.

The <length> value(s) used to express font size must be non-negative.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the closest supported value.

The tts:fontSize style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="299px 97px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="center"/>
  <style tts:textAlign="center"/>
  <style tts:fontFamily="proportionalSansSerif"/>
  <style tts:fontSize="18px"/>
</region>
...
<p region="r1">
  Then fill up the glasses<br/>
  with treacle and ink,<br/>
  Or anything else<br/>
  that is <span tts:fontSize="24px">pleasant</span> to drink.
</p>

Example Rendition – Font Size

8.2.10 tts:fontStyle

The tts:fontStyle attribute is used to specify a style property that defines the font style to apply to glyphs that are selected for glyph areas generated by content flowed into a region, where the mapping from font style value to specific font face or style parameterization is not determined by this specification.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

Use of the value oblique denotes a shear transformation (at an unspecified angle) in the inline progression dimension.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value normal.

The tts:fontStyle style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="331px 84px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
  <style tts:fontFamily="proportionalSansSerif"/>
</region>
...
<p region="r1">
  In autumn, when the leaves are brown,<br/>
  Take pen and ink, and <span tts:fontStyle="italic">write it down.</span>
</p>

Example Rendition – Font Style

8.2.11 tts:fontWeight

The tts:fontWeight attribute is used to specify a style property that defines the font weight to apply to glyphs that are selected for glyph areas generated by content flowed into a region, where the mapping from font weight value to specific font face or weight parameterization is not determined by this specification.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value normal.

The tts:fontWeight style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="376px 95px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="center"/>
  <style tts:textAlign="center"/>
  <style tts:fontFamily="proportionalSansSerif"/>
</region>
...
<p region="r1">
  They told me you had been to her,<br/>
  <span tts:fontWeight="bold">and mentioned me to him:</span><br/>
  She gave me a good character<br/>
  <span tts:fontWeight="bold">but said I could not swim.</span>
</p>

Example Rendition – Font Weight

8.2.12 tts:lineHeight

The tts:lineHeight attribute is used to specify a style property that defines the inter-baseline separation between line areas generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If the value of this attribute is normal, then the used value of this style property should be determined as follows:

1. Let P be the p element to which this style property applies.

2. Let FF be the computed value of the tts:fontFamily style property of P.

3. Let FS be the computed value of the tts:fontSize style property of P.

4. Let F0 be the first font obtained when sequentially mapping each font family in FF to a set of available fonts, where this set of available fonts is constrained as needed to satisfy the computed values of the tts:fontStyle and tts:fontWeight style properties of P.

5. If F0 is associated with font metrics that specify altitude A, descent D, and line gap G, then set LH to the sum of scaled(A), scaled(D), and scaled(G), where scaled(X) denotes font metric X scaled according to font size FS.

6. Otherwise, LH is considered to be implementation dependent; however, in the absence of implementation specific requirements, LH is recommended to be set to 125% of FS.

7. Set the used value of this style property to LH.

If specified as a <length>, then the length must be non-negative.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the closest supported value.

The tts:lineHeight style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="255px 190px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="center"/>
  <style tts:textAlign="start"/>
  <style tts:fontFamily="proportionalSansSerif"/>
  <style tts:fontSize="16px"/>
  <style tts:lineHeight="32px"/>
</region>
...
<p region="r1">
  He thought he saw an elephant,<br/>
  That practised on a fife:<br/>
  He looked again, and found it was<br/>
  A letter from his wife.<br/>
  "At length I realise," he said,<br/>
  "The bitterness of Life.
"</p>

Example Rendition – Line Height

8.2.13 tts:opacity

The tts:opacity attribute is used to specify a style property that defines the opacity (or conversely, the transparency) of marks associated with a region.

When presented onto a visual medium, the opacity of the region is applied uniformly and on a linear scale to all marks produced by content targeted to the region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

The tts:opacity style is illustrated by the following example.

<region xml:id="r1" dur="5s">
  <set begin="0s" dur="1s" tts:opacity="1.00"/>
  <set begin="1s" dur="1s" tts:opacity="0.75"/>
  <set begin="2s" dur="1s" tts:opacity="0.50"/>
  <set begin="3s" dur="1s" tts:opacity="0.25"/>
  <set begin="4s" dur="1s" tts:opacity="0.00"/>
  <style tts:extent="304px 77px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
</region>
...
<p region="r1">
  The sun was shining on the sea
</p>

Example Rendition – Opacity

8.2.14 tts:origin

The tts:origin attribute is used to specify the x and y coordinates of the origin of a region area with respect to the origin of the Root Container Region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If the value of this attribute consists of two <length> specifications, then they must be interpreted as x and y coordinates, where the first specification is the x coordinate, and the second specification is the y coordinate.

If the value of this attribute is auto, then the computed value of the style property must be considered to be the same as the origin of the Root Container Region.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the closest supported value.

The tts:origin style is illustrated by the following example.

<region xml:id="r1">
  <style tts:origin="40px 40px"/>
  <style tts:extent="308px 92px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="center"/>
  <style tts:textAlign="center"/>
</region>
...
<p region="r1">
  "To dine!" she shrieked in dragon-wrath.<br/>
  "To swallow wines all foam and froth!<br/>
   To simper at a table-cloth!"
</p>

Example Rendition – Origin

8.2.15 tts:overflow

The tts:overflow attribute is used to specify a style property that defines whether a region area is clipped or not if the descendant areas of the region overflow its extent.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If the value of this attribute is visible, then content should not be clipped outside of the affected region, and region composition and layout must be performed as if the region's width and height were unconstrained, but with a well-defined origin. If the value is hidden, then content should be clipped outside of the affected region.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value hidden.

The tts:overflow style is illustrated by the following example.

<?xml version="1.0"?>
<tt xmlns="http://www.w3.org/ns/ttml"
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    xml:lang="en"
    tts:extent="320px 240px">
  <head>
    <styling>
      <style xml:id="s1" tts:backgroundColor="black"
             tts:padding="6px"/>
      <style xml:id="s2" tts:color="red" tts:backgroundColor="white"
             tts:wrapOption="noWrap" tts:fontFamily="proportionalSansSerif"
             tts:fontSize="10px"/>
    </styling>
    <layout>
      <region xml:id="r1" style="s1" tts:extent="100px 40px"
              tts:origin="20px 20px" tts:overflow="visible"/>
      <region xml:id="r2" style="s1" tts:extent="100px 40px"
              tts:origin="20px 180px" tts:overflow="hidden"/>
    </layout>
  </head>
  <body>
    <div>
      <p region="r1" style="s2">
        "But wait a bit," the Oysters cried,<br/>
        "Before we have our chat;
      </p>
      <p region="r2" style="s2">
        For some of us are out of breath,<br/>
        And all of us are fat!"
      </p>
    </div>
  </body>
</tt>

Example Rendition – Overflow

8.2.16 tts:padding

The tts:padding attribute is used to specify padding (or inset) space on all sides of a region area.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If the value of this attribute consists of one <length> specification, then that length applies to all edges of the affected areas. If the value consists of two <length> specifications, then the first applies to the before and after edges, and the second applies to the start and end edges. If three <length> specifications are provided, then the first applies to the before edge, the second applies to the start and end edges, and the third applies to the after edge. If four <length> specifications are provided, then they apply to before, end, after, and start edges, respectively.

The <length> value(s) used to express padding must be non-negative.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the closest supported value.

The tts:padding style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="446px 104px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
  <style tts:padding="10px 40px"/>
</region>
...
<p region="r1" tts:backgroundColor="red">
  Just the place for a Snark! I have said it twice:<br/>
  That alone should encourage the crew.<br/>
  Just the place for a Snark! I have said it thrice:<br/>
  What I tell you three times is true.
</p>

When rendering an area to which padding applies, the background color that applies to the area is rendered into the padded portion of the area.

Example Rendition – Padding

8.2.17 tts:showBackground

The tts:showBackground attribute is used to specify constraints on when the background color of a region is intended to be presented.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If the value of this attribute is always, then the background color of a region is always rendered when performing presentation processing on a visual medium; if the value is whenActive, then the background color of a region is rendered only when some content is flowed into the region.

A region satisfies the whenActive case if (1) it is a Temporally Active Region and (2) content is selected into the region, where that content is also Temporally Active.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value always.

The tts:showBackground style is illustrated by the following example.

<region xml:id="r1">
  <style tts:origin="0px 0px"/>
  <style tts:extent="265px 100px"/>
  <style tts:backgroundColor="black"/>
  <style tts:showBackground="always"/>
  <style tts:color="white"/>
  <style tts:displayAlign="before"/>
  <style tts:textAlign="start"/>
</region>
<region xml:id="r2">
  <style tts:origin="205px 60px"/>
  <style tts:extent="290px 100px"/>
  <style tts:backgroundColor="red"/>
  <style tts:color="white"/>
  <style tts:displayAlign="before"/>
  <style tts:textAlign="end"/>
  <style tts:showBackground="whenActive"/>
</region>

8.2.18 tts:textAlign

The tts:textAlign attribute is used to specify a style property that defines how inline areas are aligned within a containing block area in the inline progression direction.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value start.

The tts:textAlign style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="355px 43px"/>
  <style tts:origin="0px 0px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:textAlign="start"/>
</region>
<region xml:id="r2">
  <style tts:extent="355px 43px"/>
  <style tts:origin="0px 47px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:textAlign="end"/>
</region>
...
<p region="r1">
  Beware the Jabberwock, my son!<br/>
  The jaws that bite, the claws that catch!
</p>
<p region="r2">
  Beware the Jubjub bird, and shun<br/>
  The frumious Bandersnatch!
</p>

Example Rendition – Text Align

8.2.19 tts:textDecoration

The tts:textDecoration attribute is used to specify a style property that defines a text decoration effect to apply to glyph areas or other inline areas that are generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value none.

The tts:textDecoration style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="385px 82px"/>
  <style tts:origin="0px 0px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:padding="5px 2px"/>
  <style tts:textDecoration="underline"/>
</region>
...
<p region="r1">
  The sea was wet<span tts:textDecoration="noUnderline"> as </span>wet
  <span tts:textDecoration="noUnderline">
    could be,<br/>
    The sand was dry as dry.<br/>
    <span tts:textDecoration="lineThrough">There weren't any</span>
    You <span tts:textDecoration="lineThrough">couldn't</span>
    could not see a cloud<br/>
    Because no cloud was in the sky.
  </span>
</p>

Example Rendition – Text Decoration

8.2.20 tts:textOutline

The tts:textOutline attribute is used to specify a style property that defines a text outline effect to apply to glyphs that are selected for glyph areas generated by content flowed into a region.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

The value of this attribute consists of an optional <color> term followed by one or two <length> terms. If a color term is present, then it denotes the outline color; if no color term is present, the computed value of the tts:color applies. The first length term denotes the outline thickness and the second length term, if present, indicates the blur radius.

When a relative <length> value is specified for outline thickness or blur radius, then it is resolved in terms of the height component of the referenced font size or Computed Cell Size.

The <length> value(s) used to express thickness and blur radius must be non-negative.

If no blur radius is specified, i.e., only one <length> term is present, then the computed value of 0px applies.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value none.

The tts:textOutline style is illustrated by the following example.

<region xml:id="r1">
  <style tts:backgroundColor="transparent"/>
  <style tts:color="yellow"/>
  <style tts:textOutline="black 2px 0px"/>
  <style tts:fontFamily="proportionalSansSerif"/>
  <style tts:fontSize="24px"/>
</region>
...
<p>
  How doth the little crocodile<br/>
  Improve its shining tail,<br/>
  And pour the waters of the Nile<br/>
  On every golden scale!<br/>
  How cheerfully he seems to grin,<br/>
  How neatly spreads his claws,<br/>
  And welcomes little fishes in,<br/>
  With gently smiling jaws!
</p>

Example Rendition – Text Outline

8.2.21 tts:unicodeBidi

The tts:unicodeBidi attribute is used to specify a style property that defines a directional embedding or override according to the Unicode bidirectional algorithm.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value normal.

The tts:unicodeBidi style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="265px 84px"/>
  <style tts:padding="5px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:textAlign="center"/>
</region>
...
<p region="r1">
  Little birds are playing<br/>
  Bagpipes on the shore,<br/>
  <span tts:unicodeBidi="bidiOverride" tts:direction="rtl">where the tourists snore.</span>
</p>

Example Rendition – Unicode Bidirectionality

8.2.22 tts:visibility

The tts:visibility attribute is used to specify a style property that defines whether generated areas are visible or not when rendered on a visual presentation medium.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

The tts:visibility style has no affect on content layout or composition, but merely determines whether composed content is visible or not.

If the computed value of the property associated with this attribute is visible, then areas generated by this element are rendered visible when presented on a visual medium. If the computed value is hidden, then they are not rendered visible, i.e., they are hidden; notwithstanding the foregoing, a descendant element of a hidden element is rendered visible if the computed value of this property is visible on the descendant.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value visible.

The tts:visibility style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="398px 121px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style/>
</region>
...
<p region="r1" dur="4s">
  <span tts:visibility="hidden">
    <set begin="1s" tts:visibility="visible"/>
    Curiouser
  </span>
  <span tts:visibility="hidden">
    <set begin="2s" tts:visibility="visible"/>
    and
  </span>
  <span tts:visibility="hidden">
    <set begin="3s" tts:visibility="visible"/>
    curiouser!
  </span>
</p>

Example Rendition – Visibility

8.2.23 tts:wrapOption

The tts:wrapOption attribute is used to specify a style property that defines whether or not automatic line wrapping (breaking) applies within the context of the affected element.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

For the purpose of determining applicability of this style property, each character child of a p element is considered to be enclosed in an anonymous span.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value wrap.

The tts:wrapOption style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="192px 117px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:displayAlign="after"/>
  <style tts:overflow="hidden"/>
  <style tts:wrapOption="noWrap"/>
</region>
...
<p>
  I'll tell thee everything I can:<br/>
  There's little to relate.<br/>
  I saw an aged aged man,<br/>
  A-sitting on a gate.
</p>

Example Rendition – Wrap Option

8.2.24 tts:writingMode

The tts:writingMode attribute is used to specify a style property that defines the block and inline progression directions to be used for the purpose of stacking block and inline areas within a region area.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the value lrtb.

The tts:writingMode style is illustrated by the following example.

<region xml:id="r1">
  <style tts:extent="50px 570px"/>
  <style tts:origin="0px 0px"/>
  <style tts:padding="10px 3px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:writingMode="tbrl"/>
</region>
<region xml:id="r2">
  <style tts:extent="310px 50px"/>
  <style tts:origin="70px 120px"/>
  <style tts:padding="10px 3px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:writingMode="rltb"/>
</region>
...
<p region="r1">
  I sometimes dig for buttered rolls,<br/>
  Or set limed twigs for crabs:
</p>
<p region="r2" tts:direction="rtl" tts:unicodeBidi="bidiOverride">
  I sometimes search the grassy knolls for the wheels of Hansom-cabs.
</p>

Example Rendition – Writing Mode

8.2.25 tts:zIndex

The tts:zIndex attribute is used to specify a style property that defines the front-to-back ordering of region areas in the case that they overlap.

This attribute may be specified by any element type that permits use of attributes in the TT Style Namespace; however, this attribute applies as a style property only to those element types indicated in the following table.

If two areas are associated with the same Z-index value, then, if those areas overlap in space, the area(s) generated by lexically subsequent elements must be rendered over area(s) generated by lexically prior elements, where lexical order is defined as the postorder traversal of a Document Instance.

The tt element is considered to establish the root of the stacking context, as defined by [XSL 1.1], § 7.30.18.

If a computed value of the property associated with this attribute is not supported, then a presentation processor must use the closest supported value.

The tts:zIndex style is illustrated by the following example.

<region xml:id="r1">
  <style tts:origin="0px 0px"/>
  <style tts:extent="400px 100px"/>
  <style tts:padding="5px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:zIndex="0"/>
</region>
<region xml:id="r2">
  <style tts:origin="100px 60px"/>
  <style tts:extent="400px 100px"/>
  <style tts:padding="5px"/>
  <style tts:backgroundColor="red"/>
  <style tts:color="white"/>
  <style tts:textAlign="end"/>
  <style tts:zIndex="1"/>
</region>
<region xml:id="r3">
  <style tts:origin="0px 120px"/>
  <style tts:extent="400px 100px"/>
  <style tts:padding="5px"/>
  <style tts:backgroundColor="black"/>
  <style tts:color="white"/>
  <style tts:zIndex="2"/>
</region>
<region xml:id="r4">
  <style tts:origin="100px 180px"/>
  <style tts:extent="400px 100px"/>
  <style tts:padding="5px"/>
  <style tts:backgroundColor="red"/>
  <style tts:color="white"/>
  <style tts:textAlign="end"/>
  <style tts:zIndex="3"/>
</region>
...
<p region="r1">
  I passed by his garden, and marked, with one eye,<br/>
  How the Owl and the Panther were sharing a pie.
</p>
<p region="r2">
  The Panther took pie-crust, and gravy, and meat,<br/>
  While the Owl had the dish as its share of the treat.
</p>
<p region="r3">
  When the pie was all finished, the Owl, as a boon,<br/>
  Was kindly permitted to pocket the spoon:
</p>
<p region="r4">
  While the Panther received knife and fork<br/>
  with a growl,<br/>
  And concluded the banquet by...
</p>

Example Rendition – Z Index

8.3.1 <alpha>

An <alpha> expression is used to express an opacity value, where 0 means fully transparent and 1 means fully opaque.

<alpha>
  : float

In the above syntax representation, the syntactic element float must adhere to the lexical representation defined by [XML Schema Part 2] § 3.2.4.1. If the value represented is less than 0.0, then it must be interpreted as equal to 0.0; similarly, if the value represented is greater than 1.0, then it must be interpreted as 1.0. The value NaN must be interpreted as 0.0.

A specified value for <alpha> should not be NaN, less than 0, or greater than 1.

If a presentation processor does not support a specific, valid opacity value, then it must interpret it as being equal to the closest supported value.

8.3.2 <color>

A <color> expression is used to specify a named color, exact RGB color triple, or exact RGBA color tuple, where the alpha component, if expressed, is maximum (255) at 100% opacity and minimum (0) at 0% opacity, and where the applicable color space is defined by [SRGB].

<color>
  : "#" rrggbb
  | "#" rrggbbaa
  | "rgb(" r-value "," g-value "," b-value ")"
  | "rgba(" r-value "," g-value "," b-value "," a-value ")"
  | <namedColor>

rrggbb
  :  <hexDigit>{6}

rrggbbaa
  :  <hexDigit>{8}

r-value | g-value | b-value | a-value
  : component-value

component-value
  : non-negative-integer                    // valid range: [0,255]

non-negative-integer
  : <digit>+

When expressing RGB component values, these values are considered to not be premultiplied by alpha.

For the purpose of performing presentation processing such that non-opaque or non-transparent alpha or opacity values apply, then the semantics of compositing functions are defined with respect to the use of the [SRGB] color space for both inputs and outputs of the composition function.

If a presentation processor does not support a specific, valid color or alpha value, then it must interpret it as being equal to the closest supported value.

8.3.3 <digit>

A <digit> is used to express integers and other types of numbers or tokens.

<digit>
  : "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

8.3.4 <duration>

This section is non-normative.

8.3.5 <familyName>

A <familyName> expression specifies a font family name.

<familyName>
  : unquoted-string
  | quoted-string

unquoted-string
  : identifier ( lwsp identifier )*

lwsp
  : ( ' ' | '\t' | '\n' | '\r' )+

identifier
  : [-]? identifier-start identifier-following*

identifier-start
  : [_a-zA-Z]
  | non-ascii-or-c1
  | escape

identifier-following
  : [_a-zA-Z0-9-]
  | non-ascii-or-c1
  | escape

non-ascii-or-c1
  : [^\0-\237]

escape
  : '\\' char

quoted-string
  : double-quoted-string
  | single-quoted-string

double-quoted-string
  : '"' ( [^"\\] | escape )+ '"'

single-quoted-string
  : "'" ( [^'\\] | escape )+ "'"

In addition to adhering to the syntax rules specified above, the following semantic rules apply:

• the semantic value of a <familyName> expression is the semantic value of its unquoted-string or quoted-string non-terminal, according to whichever applies;

• the semantic value of an unquoted-string non-terminal is a pair <quoted, content>, where quoted is a boolean false, and where content is the result of appending the value of each identifier non-terminal, in lexical order, where the value of each identifier is preceded by a single SPACE (U+0020) character if it is not the first identifier;

• the semantic value of a quoted-string non-terminal is a pair <quoted, content>, where quoted is a boolean true, and where content is the unquoted content of the quoted string, i.e., the sequence of characters between the delimiting quotes.

• the semantic value of an escape non-terminal is the value of the escaped char;

• a <familyName> that takes the form of an unquoted-string that contains an identifier that starts with two - HYPHEN-MINUS (U+002D) characters must be considered to be invalid;

• a <familyName> that takes the form of an unquoted-string that contains a single identifier that matches (by case sensitive comparison) a <genericFamilyName> must be interpreted as that <genericFamilyName>;

• a <familyName> that takes the form of a quoted-string whose content (unquoted value) matches (by case sensitive comparison) a <genericFamilyName> must not be interpreted as that <genericFamilyName>, but as the actual name of a non-generic font family.

8.3.6 <genericFamilyName>

A <genericFamilyName> expression specifies a font family using a general token that indicates a class of font families.

The resolution of a generic family name to a concrete font instance is considered to be implementation dependent, both in the case of content authoring and content interpretation.

<genericFamilyName>
  : "default"
  | "monospace"
  | "sansSerif"
  | "serif"
  | "monospaceSansSerif"
  | "monospaceSerif"
  | "proportionalSansSerif"
  | "proportionalSerif"

The mapping between a generic (font) family name and an actual font is not determined by this specification; however, the distinction of monospace versus proportional and serif versus sans-serif should be maintained if possible when performing presentation.

If a generic (font) family name of monospace is specified, then it may be interpreted as equivalent to either monospaceSansSerif or monospaceSerif. The generic family names sansSerif and serif are to be interpreted as equivalent to proportionalSansSerif and proportionalSerif, respectively.

If the generic family name default is specified (or implied by an initial value), then its typographic characteristics are considered to be implementation dependent; however, it is recommended that this default font family be mapped to a monospaced, sans-serif font.

8.3.7 <hexDigit>

A <hexDigit> is used to express integers and other types of numbers or tokens that employ base 16 arithmetic.

For the purpose of parsing, a distinction must not be made between lower and upper case.

<hexDigit>
  : <digit>
  | "a" | "b" | "c" | "d" | "e" | "f"
  | "A" | "B" | "C" | "D" | "E" | "F"

8.3.8 <integer>

An <integer> expression is used to express an arbitrary, signed integral value.

<integer>
  : ( "+" | "-" )? <digit>+

8.3.9 <length>

A <length> expression is used to express either a coordinate component of point in a cartesian space or a distance between two points in a cartesian space.

<length>
  : scalar
  | percentage

scalar
  : number units

percentage
  : number "%"

sign
  : "+" | "-"

number
  : sign? non-negative-number

non-negative-number
  : non-negative-integer
  | non-negative-real

non-negative-integer
  : <digit>+

non-negative-real
  : <digit>* "." <digit>+

units
  : "px"
  | "em"
  | "c"                                     // abbreviation of "cell"

It is an error to omit the units component of a scalar length value.

The semantics of the unit of measure px (pixel) are as defined by [XSL 1.1], § 5.9.13.

When specified relative to a font whose size is expressed as a single length measure or as two length measures of equal length, the unit of measure em is considered to be identical to that defined by [XSL 1.1], § 5.9.13; however, when specified relative to a font whose size is expressed as two length measures of non-equal lengths, then one em is equal to the inline progression dimension of the anamorphically scaled font when used to specify lengths in the inline progression direction and equal to the block progression dimension of the scaled font when used to specify lengths in the block progression direction.

The semantics of the unit of measure c (cell) are defined by the parameter 6.2.1 ttp:cellResolution.

8.3.10 <namedColor>

A <namedColor> is used to express an RGBA color with a convenient name, and where the applicable color space is defined by [SRGB].

For the purpose of parsing, a distinction must not be made between lower and upper case.

<namedColor>
  : "transparent"                           // #00000000
  | "black"                                 // #000000ff
  | "silver"                                // #c0c0c0ff
  | "gray"                                  // #808080ff
  | "white"                                 // #ffffffff
  | "maroon"                                // #800000ff
  | "red"                                   // #ff0000ff
  | "purple"                                // #800080ff
  | "fuchsia"                               // #ff00ffff
  | "magenta"                               // #ff00ffff (= fuchsia)
  | "green"                                 // #008000ff
  | "lime"                                  // #00ff00ff
  | "olive"                                 // #808000ff
  | "yellow"                                // #ffff00ff
  | "navy"                                  // #000080ff
  | "blue"                                  // #0000ffff
  | "teal"                                  // #008080ff
  | "aqua"                                  // #00ffffff
  | "cyan"                                  // #00ffffff (= aqua)

8.3.11 <quotedString>

This section is non-normative.

8.3.12 <string>

This section is non-normative.

8.4.1 Style Association

Style association is a sub-process of 8.4.4 Style Resolution Processing used to determine the specified style set of each content and layout element.

Style matter may be associated with content and layout matter in a number of ways:

• inline styling

• referential styling

• chained referential styling

In addition to the above, style matter may be associated with layout matter using:

• nested styling

<p tts:color="white">White 1 <span tts:color="yellow">Yellow</span> White 2</p>

<style xml:id="s1" tts:color="white"/>
<style xml:id="s2" tts:color="yellow"/>
...
<p style="s1">White 1 <span style="s2">Yellow</span> White 2</p>

<style xml:id="s1" tts:color="white" tts:fontFamily="monospaceSerif"/>
<style xml:id="s2" style="s1" tts:color="yellow"/>
...
<p style="s1">White Monospace</p>
<p style="s2">Yellow Monospace</p>

<region xml:id="r1">
  <style tts:extent="128px 66px"/>
  <style tts:origin="0px 0px"/>
  <style tts:displayAlign="center"/>
</region>

8.4.2 Style Inheritance

Style inheritance is a sub-process of 8.4.4 Style Resolution Processing used to determine the specified style set of each content and layout element.

Styles are further propagated to content matter using:

• content style inheritance

• region style inheritance

For the purpose of determining inherited styles, the element hierarchy of an intermediate synchronic document form of a Document Instance must be used, where such intermediate forms are defined by 9.3.3 Intermediate Synchronic Document Construction.

<p tts:fontFamily="monospaceSansSerif">
  <span tts:color="yellow">Yellow Monospace</span>
</p>

<region xml:id="r1">
  <style tts:color="yellow"/>
  <style tts:fontFamily="monospaceSerif"/>
</region>
...
<p region="r1">Yellow Monospace</p>

8.4.3 Style Resolution Value Categories

During style resolution, layout, and presentation processing, three categories of style property values are distinguished as follows:

• specified values

• computed values

• used values

• actual values

8.4.4 Style Resolution Processing

The process of style resolution is defined herein as the procedure (and results thereof) for resolving (determining) the computed values of all style properties that apply to content and layout elements:

• 8.4.4.1 Conceptual Definitions

• 8.4.4.2 Specified Style Set Processing

• 8.4.4.3 Computed Style Set Processing

• 8.4.4.4 Style Resolution Process

The process described here forms an integral sub-process of 9.3 Region Layout and Presentation.

9.1.1 layout

The layout element is a container element used to group layout matter, including metadata that applies to layout matter.

The layout element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more region elements.

<layout
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, region*
</layout>

To the extent that time semantics apply to the content of the layout element, the implied time interval of this element is defined to be coterminous with the Root Temporal Extent.

9.1.2 region

The region element is used to define a rectangular space or area into which content is to be flowed for the purpose of presentation.

In addition, and in accordance with 8.4.2.2 Region Style Inheritance, the region element may be used to specify inheritable style properties to be inherited by content that is flowed into it.

The region element accepts as its children zero or more elements in the Metadata.class element group, followed by zero or more elements in the Animation.class element group, followed by zero or more style elements.

Any metadata specified by children in the Metadata.class element group applies semantically to the region element and its descendants as a whole. Any animation elements specified by children in the Animation.class element group apply semantically to the region element. Any style child element must be considered a local style definition that applies only to the containing region element, i.e., does not apply for resolving referential styling (but does apply for region style inheritance).

<region
  begin = <timeExpression>
  dur = <timeExpression>
  end = <timeExpression>
  style = IDREFS
  timeContainer = (par|seq)
  ttm:role = string
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*, Animation.class*, style*
</region>

If begin and (or) end attributes are specified on a region element, then they specify the beginning and (or) ending points of a time interval during which the region is eligible for activation and with respect to which animation child elements of the region are timed. If specified, these begin and end points are relative to the time interval of the nearest ancestor element associated with a time interval, irregardless of whether that interval is explicit or implied.

The nearest ancestor element of a region element that is associated with a time interval is the layout element.

If a dur attribute is specified on the region element, then it specifies the simple duration of the region.

For the purpose of determining the semantics of presentation processing, a region that is temporally inactive must not produce any visible marks when presented on a visual medium.

If no timeContainer attribute is specified on a region element, then it must be interpreted as having parallel time containment semantics.

If a ttm:role attribute is specified on a region element, then it must adhere to the value syntax defined by Syntax Representation – ttm:role, and where the roles identified by this attribute express the semantic roles of the region independently from the semantic roles of any content targeted to (associated with) the region.

9.2.1 region

The region attribute is used to reference a region element which defines a space or area into which a Content element is intended to be flowed.

If specified, the value of a region attribute must adhere to the IDREF data type defined by [XML Schema Part 2], § 3.3.9, and, furthermore, this IDREF must reference a region element which has a layout element as an ancestor.

The region attribute may be specified by an instance of the following element types:

• body

• div

• p

• span

9.3.1 Default Region

If a Document Instance does not specify a region element, then a default region is implied with the following characteristics:

• the identity of the default region is considered to be anonymous;

• the extent of the default region is the same as the extent of the Root Container Region;

• the temporal interval of the default region is the same as the interval defined by the Root Temporal Extent;

Furthermore, if no region element is specified, then the region attribute must not be specified on any Content element in the Document Instance.

If a default region is implied for a given Document Instance, then the body element is implicitly targeted to (associated with) the default region.

When implying a default region, the Document Instance is to be treated as if a region element and its parent layout element were specified in a head element, and a matching region attribute were specified on the body element as shown in the following example:

<tt xml:lang="" xmlns="http://www.w3.org/ns/ttml">
  <head>
    <layout>
      <region xml:id="anonymous"/>
    </layout>
  </head>
  <body region="anonymous"/>
</tt>

9.3.2 Anonymous Span Construction

For the purposes of performing presentation processing, anonymous spans are created according to the following [construct anonymous spans] procedure:

[construct anonymous spans]

1. for each significant text node in a Content element, synthesize an anonymous span to enclose the text node, substituting the new anonymous span for the original text node child in its sibling and parent hierarchy;

2. for each contiguous sequence of anonymous spans, replace the sequence with a single anonymous span which contains a sequence of text nodes representing the individual text node children of the original sequence of anonymous spans;

3. for each span element whose child is a single anonymous span, replace the anonymous span with its sequence of child text nodes;

9.3.3 Intermediate Synchronic Document Construction

For the purposes of performing presentation processing, the active time duration of a Document Instance is divided into a sequence of time coordinates where at each time coordinate, some element becomes temporally active or inactive, then, at each such time coordinate, a Document Instance is mapped from its original, source form, DOC_source , to an intermediate synchronic document form, DOC_inter , according to the [construct intermediate document] procedure:

[construct intermediate document]

1. for each temporally active region R, replicate the sub-tree of DOC_source headed by the body element;

2. evaluating this sub-tree in a postorder traversal, prune elements if any of the following conditions is true:

   1. they are neither Content nor Animation elements; or

   2. they are temporally inactive; or

   3. they are empty and neither Animation elements nor br elements; or

   4. they are Content elements and aren't associated with region R according to the [associate region] procedure.

3. if the pruned sub-tree is non-empty, then reparent it to the R element;

4. finally, after completing the above steps, prune the original body element from the intermediate document, then prune all region, begin, end, and dur attributes, which are no longer semantically relevant;

Note:

In this section, the term prune, when used in reference to an element, means that the element is to be removed from its parent's children, which, in turn, implies that the descendants of the pruned element will no longer be descendants of the element's parent. When prune is used in reference to an attribute, it means that attribute is to be removed from its associated (owning) element node.

[associate region]

A Content element is associated with a region according to the following ordered rules, where the first rule satisfied is used and remaining rules are skipped:

1. if the element specifies a region attribute, then the element is associated with the region referenced by that attribute;

2. if some ancestor of that element specifies a region attribute, then the element is associated with the region referenced by the most immediate ancestor that specifies this attribute;

3. if the element contains a descendant element that specifies a region attribute, then the element is associated with the region referenced by that attribute;

4. if a default region was implied (due to the absence of any region element), then the element is associated with the default region;

5. the element is not associated with any region.

The result of performing the processing described above will be a sequence of N intermediate synchronic Document Instances, DOC_inter0 … DOC_interN−1.

9.3.4 Synchronic Flow Processing

Subsequent to performing a temporal (synchronic) slice and subsequent remapping of regionally selected content hierarchy, the resulting intermediate synchronic document is subjected to a flow transformation step that produces a rooted flow object tree represented as an XSL FO document instance as defined by [XSL 1.1], and semantically extended by TTML specific style properties that have no XSL FO counterpart.

Each intermediate synchronic document produced by 9.3.3 Intermediate Synchronic Document Construction is mapped to an XSL FO document instance, F, as follows:

1. perform the [construct anonymous spans] procedure;

2. resolve styles according to 8.4.4.4 Style Resolution Process;

3. map the tt element to an fo:root element, populated initially with an fo:layout-master-set element that contains a valid fo:simple-page-master that, in turn, contains an fo:region-body child, where the extent of the Root Container Region expressed on the tt element is mapped to page-width and page-height attributes on the fo:simple-page-master element;

4. map the layout element to an fo:page-sequence element and a child fo:flow element that reference the page master and page region defined by the simple page master produced above;

5. map each non-empty region element to an fo:block-container element with an absolute-position attribute with value absolute, with top, left, bottom, and right attributes that express a rectangle equivalent to the region's origin, extent (including padding), and with a line-stacking-strategy attribute with value line-height;

   Note:

   The region's extent corresponds with the allocation rectangle of the block area generated by the fo:block-container.

6. for each body, div, and p element that is not associated with a tts:display style property with the value none, map the element to a distinct fo:block element, populating the style properties of fo:block by using the computed style set associated with each original TTML Content element;

7. for the resulting fo:block formatting object produced in the previous step that corresponds to the body element, perform the following ordered sub-steps:

   1. if the display-align style property of this fo:block has the value center or after, then synthesize and insert as the first child of this fo:block an empty fo:block with the following attributes: space-after.optimum, space-after.maximum, and space-after.conditionality, where the value of the former two attributes is the height or width of the containing fo:block-container element, whichever of these is designated as the block progression dimension, and where the value of the last is retain;

   2. if the display-align style property of this fo:block has the value center or before, then synthesize and insert as the last child of this fo:block an empty fo:block with the following attributes: space-after.optimum, space-after.maximum, and space-after.conditionality, where the value of the former two attributes is the height or width of the containing fo:block-container element, whichever of these is designated as the block progression dimension, and where the value of the last is retain;

8. for each span element that is not associated with a tts:display style property with the value none and for each anonymous span that is a child of a p or span element, map the element or sequence of character items to a distinct fo:inline element, populating the style properties of fo:inline by using the computed style set associated with each original TTML Content element or anonymous span;

9. for each br element that is not associated with a tts:display style property with the value none, map the element to a distinct fo:character element having the following properties:

   • character="
"

   • suppress-at-line-break="retain"

10. for each TTML style property attribute in some computed style set that has no counterpart in [XSL 1.1], map that attribute directly through to the relevant formatting object produced by the input TTML Content element to which the style property applies;

11. optionally, synthesize a unique id attribute on each resulting formatting object element that relates that element to the input element that resulted in that formatting object element;

For each resulting document instance F, if processing requires presentation on a visual medium, then apply formatting and rendering semantics consistent with that prescribed by [XSL 1.1].

9.3.5 Elaborated Example (Informative)

An example of the processing steps described above is elaborated below, starting with Example – Sample Source Document.

<tt tts:extent="640px 480px" xml:lang="en"
  xmlns="http://www.w3.org/ns/ttml"
  xmlns:tts="http://www.w3.org/ns/ttml#styling">
  <head>
    <layout>
      <region xml:id="r1">
        <style tts:origin="10px 100px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="red"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
      </region>
      <region xml:id="r2">
        <style tts:origin="10px 300px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="yellow"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
      </region>
    </layout>
  </head>
  <body xml:id="b1">
    <div xml:id="d1" begin="0s" dur="2s">
      <p xml:id="p1" region="r1">Text 1</p>
      <p xml:id="p2" region="r2">Text 2</p>
    </div>
    <div xml:id="d2" begin="1s" dur="2s">
      <p xml:id="p3" region="r2">Text 3</p>
      <p xml:id="p4" region="r1">Text 4</p>
    </div>
  </body>
</tt>

In the above document, the content hierarchy consists of two divisions, each containing two paragraphs. This content is targeted (associated with) one of two non-overlapping regions that are styled identically except for their position and their foreground colors, the latter of which is inherited by and applies to the (and, in this case, anonymous) spans reparented into the regions.

The following, first intermediate document shows the synchronic state for time interval [0,1), during which time only division d1 is temporally active, and where paragraphs p1 and p2 (and their ancestors) are associated with regions r1 and r2, respectively.

<tt tts:extent="640px 480px" xml:lang="en"
  xmlns="http://www.w3.org/ns/ttml"
  xmlns:tts="http://www.w3.org/ns/ttml#styling">
  <head>
    <layout>
      <region xml:id="r1">
        <style tts:origin="10px 100px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="red"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
        <body xml:id="b1-1">
          <div xml:id="d1-1">
            <p xml:id="p1">Text 1</p>
          </div>
        </body>
      </region>
      <region xml:id="r2">
        <style tts:origin="10px 300px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="yellow"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
        <body xml:id="b1-2">
          <div xml:id="d1-2">
            <p xml:id="p2">Text 2</p>
          </div>
        </body>
      </region>
    </layout>
  </head>
</tt>

An XSL FO document instance that would yield rendering consistent with TTML, and which may be produced by performing flow processing upon the first intermediate document is illustrated below.

<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="m1"
      page-width="640px" page-height="480px">
      <fo:region-body/>
    </fo:simple-page-master>
  </fo:layout-master-set>
  <fo:page-sequence master-reference="m1">
    <fo:flow flow-name="xsl-region-body">
      <!-- region (r1) -->
      <fo:block-container id="r1" absolute-position="absolute"
        left="10px" top="100px" width="620px" height="96px"
        background-color="black" display-align="center">
        <!-- body (b1) -->
        <fo:block id="b1-1">
          <!-- body's space (before) filler -->
          <fo:block
            space-after.optimum="96px"
            space-after.maximum="96px"
            space-after.conditionality="retain"/>
          <!-- div (d1) -->
          <fo:block id="d1-1">
            <!-- p (p1) -->
            <fo:block id="p1" text-align="center">
              <fo:inline font-size="40px" font-weight="bold"
              color="red">Text 1</fo:inline>
            </fo:block>
          </fo:block>
          <!-- body's space (after) filler -->
          <fo:block
            space-after.optimum="96px"
            space-after.maximum="96px"
            space-after.conditionality="retain"/>
        </fo:block>
      </fo:block-container>
      <!-- region (r2) -->
      <fo:block-container id="r2" absolute-position="absolute"
        left="10px" top="300px" width="620px" height="96px"
        background-color="black" display-align="center">
        <!-- body (b1) -->
        <fo:block id="b1-2">
          <!-- body's space (before) filler -->
          <fo:block
            space-after.optimum="96px"
            space-after.maximum="96px"
            space-after.conditionality="retain"/>
          <!-- div (d1) -->
          <fo:block id="d1-2">
            <!-- p (p2) -->
            <fo:block id="p2" text-align="center">
              <fo:inline font-size="40px" font-weight="bold"
              color="yellow">Text 2</fo:inline>
            </fo:block>
          </fo:block>
          <!-- body's space (after) filler -->
          <fo:block
            space-after.optimum="96px"
            space-after.maximum="96px"
            space-after.conditionality="retain"/>
        </fo:block>
      </fo:block-container>
    </fo:flow>
  </fo:page-sequence>
</fo:root>

The following, second intermediate document shows the synchronic state for time interval [1,2), during which time both divisions d1 and d2 are temporally active, and where paragraphs p1 and p4 (and their ancestors) are associated with region r1 and paragraphs p2 and p3 (and their ancestors) are associated with region r2.

<tt tts:extent="640px 480px" xml:lang="en"
  xmlns="http://www.w3.org/ns/ttml"
  xmlns:tts="http://www.w3.org/ns/ttml#styling">
  <head>
    <layout>
      <region xml:id="r1">
        <style tts:origin="10px 100px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="red"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
        <body xml:id="b1-1">
          <div xml:id="d1-1">
            <p xml:id="p1">Text 1</p>
          </div>
          <div xml:id="d2-1">
            <p xml:id="p4">Text 4</p>
          </div>
        </body>
      </region>
      <region xml:id="r2">
        <style tts:origin="10px 300px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="yellow"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
        <body xml:id="b1-2">
          <div xml:id="d1-2">
            <p xml:id="p2">Text 2</p>
          </div>
          <div xml:id="d2-2">
            <p xml:id="p3">Text 3</p>
          </div>
        </body>
      </region>
    </layout>
  </head>
</tt>

The following, third intermediate document shows the synchronic state for time interval [2,3), during which time only division d2 is temporally active, and where paragraphs p4 and p3 (and their ancestors) are associated with regions r1 and r2, respectively.

<tt tts:extent="640px 480px" xml:lang="en"
  xmlns="http://www.w3.org/ns/ttml"
  xmlns:tts="http://www.w3.org/ns/ttml#styling">
  <head>
    <layout>
      <region xml:id="r1">
        <style tts:origin="10px 100px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="red"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
        <body xml:id="b1-1">
          <div xml:id="d2-1">
            <p xml:id="p4">Text 4</p>
          </div>
        </body>
      </region>
      <region xml:id="r2">
        <style tts:origin="10px 300px"/>
        <style tts:extent="620px 96px"/>
        <style tts:fontSize="40px"/>
        <style tts:fontWeight="bold"/>
        <style tts:backgroundColor="black"/>
        <style tts:color="yellow"/>
        <style tts:textAlign="center"/>
        <style tts:displayAlign="center"/>
        <body xml:id="b1-2">
          <div xml:id="d2-2">
            <p xml:id="p3">Text 3</p>
          </div>
        </body>
      </region>
    </layout>
  </head>
</tt>

10.2.1 begin

The begin attribute is used to specify the begin point of a temporal interval associated with a timed element. If specified, the value of a begin attribute must adhere to a <timeExpression> specification as defined by 10.3.1 <timeExpression>.

The begin point of a temporal interval is included in the interval; i.e., the interval is left-wise closed.

The semantics of the begin attribute are those defined by [SMIL 2.1], § 10.4.1, while taking into account any overriding semantics defined by this specification.

10.2.2 end

The end attribute is used to specify the ending point of a temporal interval associated with a timed element. If specified, the value of an end attribute must adhere to a <timeExpression> specification as defined by 10.3.1 <timeExpression>.

The ending point of a temporal interval is not included in the interval; i.e., the interval is right-wise open.

The presentation effects of a non-empty active temporal interval include the frame immediately prior to the frame (or tick) equal to or immediately following the time specified by the ending point, but do not extend into this latter frame (or tick).

The semantics of the end attribute are those defined by [SMIL 2.1], § 10.4.1, while taking into account any overriding semantics defined by this specification.

10.2.3 dur

The dur attribute is used to specify the duration of a temporal interval associated with a timed element. If specified, the value of a dur attribute must adhere to a <timeExpression> specification as defined by 10.3.1 <timeExpression>.

When a Document Instance specifies the use of the smpte time base and discontinuous marker mode, a (well-formed) dur attribute must not be specified on any element.

The semantics of the dur attribute are those defined by [SMIL 2.1], § 10.4.1, while taking into account any overriding semantics defined by this specification. In a deliberate divergence from [SMIL 2.1], § 10.4.1, the value of the dur attribute is permitted to be zero (0).

10.2.4 timeContainer

The timeContainer attribute is used to specify a local temporal context by means of which timed child elements are temporally situated.

If specified, the value of a timeContainer attribute must be one of the following:

• par

• seq

If the time container semantics of an element instance is par, then the temporal intervals of child elements are considered to apply in parallel, i.e., simultaneously in time. Furthermore, the specification of the time interval of each child element is considered to be relative to the temporal interval of the container element instance. For the purpose of determining the [SMIL 2.1] endsync semantics of a par time container, a default value of all applies.

If the time container semantics of an element instance is seq, then the temporal intervals of child elements are considered to apply in sequence, i.e., sequentially in time. Furthermore, the specification of the time interval of each child element is considered to be relative to the temporal interval of its sibling elements, unless it is the first child element, in which case it is considered to be relative to the temporal interval of the container element instance.

Each time container is considered to constitute an independent time base, i.e., time coordinate system.

If a timeContainer attribute is not specified on an element that has time container semantics, then par time container semantics must apply.

Time container semantics applies only to the following element types:

• body

• div

• p

• region

• span

The semantics of parallel and sequential time containment are those defined by [SMIL 2.1], § 10.4.2, while taking into account any overriding semantics defined by this specification.

10.3.1 <timeExpression>

A <timeExpression> is used to specify a coordinate within some time base, where the applicable time base is determined by the ttp:timeBase parameter, and where the semantics defined by N Time Expression Semantics apply.

<timeExpression>
  : clock-time
  | offset-time

clock-time
  : hours ":" minutes ":" seconds ( fraction | ":" frames ( "." sub-frames )? )?

offset-time
  : time-count fraction? metric

hours
  : <digit> <digit>
  | <digit> <digit> <digit>+

minutes | seconds
  : <digit> <digit>

frames
  : <digit> <digit>
  | <digit> <digit> <digit>+

sub-frames
  : <digit>+

fraction
  : "." <digit>+

time-count
  : <digit>+

metric
  : "h"                 // hours
  | "m"                 // minutes
  | "s"                 // seconds
  | "ms"                // milliseconds
  | "f"                 // frames
  | "t"                 // ticks

If a <timeExpression> is expressed in terms of a clock-time, then leading zeroes are used when expressing hours, minutes, seconds, and frames less than 10. Minutes are constrained to [0…59], while seconds (including any fractional part) are constrained to the closed interval [0,60], where the value 60 applies only to leap seconds. Except when ttp:timeBase is clock and ttp:clockMode is local or utc, use of the special value of 60 seconds to denote a leap second is undefined and should not be used.

If a <timeExpression> is expressed in terms of a clock-time and a frames term is specified, then the value of this term must be constrained to the interval [0…F-1], where F is the frame rate determined by the ttp:frameRate parameter as defined by 6.2.4 ttp:frameRate. It is considered an error if a frames term or f (frames) metric is specified when the clock time base applies.

If a <timeExpression> is expressed in terms of a clock-time and a sub-frames term is specified, then the value of this term must be constrained to the interval [0…S-1], where S is the sub-frame rate determined by the ttp:subFrameRate parameter as defined by 6.2.9 ttp:subFrameRate. It is considered an error if a sub-frames term is specified when the clock time base applies.

If the governing time base is smpte, then (1) the offset-time form is not defined and should not be used, and (2) the fraction seconds component in a clock-time form is not defined and should not be used.

11.1.1 set

The set element is used as a child element of a Content element or a region element in order to express a discrete change of some style parameter value that applies over some time interval.

The set element accepts as its children zero or more elements in the Metadata.class element group.

<set
  begin = <timeExpression>
  dur = <timeExpression>
  end = <timeExpression>
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {a single attribute in TT Style namespace}
  {any attribute not in default or any TT namespace}>
  Content: Metadata.class*
</set>

An example of using the set element to animate content styling is illustrated below:

...
<p dur="5s" tts:color="yellow">
<set begin="1s" dur="1s" tts:color="red"/>
<set begin="2s" dur="1s" tts:color="green"/>
<set begin="3s" dur="1s" tts:color="red"/>
Text with Flashing Colors!
</p>
...

An example of using the set element to animate region styling is illustrated below:

<tt xml:lang="" xmlns="http://www.w3.org/ns/ttml"
    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
    xmlns:tts="http://www.w3.org/ns/ttml#styling"
    ttp:cellResolution="40 16">
    <head>
      <layout>
	<region xml:id="r1" timeContainer="seq">
	  <set dur="10s" tts:origin=" 8c 14c"/>
	  <set dur="2s"  tts:origin=" 2c  2c"/>
	  <set dur="3s"  tts:origin=" 8c 14c"/>
	  <set dur="2s"  tts:origin="14c  4c"/>
	  <set dur="10s" tts:origin=" 8c 14c"/>
	  <style tts:extent="24c 2c"/>
	</region>
      </layout>
    </head>
    <body region="r1">...</body>
</tt>

12.1.1 metadata

The metadata element functions as a generic container for metadata information.

Metadata information may be expressed with a metadata element by specifying (1) one or more metadata attributes on the metadata element, (2) one or more metadata child elements in the metadata element, or (3) a combination of metadata attributes and metadata child elements. Both types of metadata information are referred to in this document as metadata items.

<metadata
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute in TT Metadata namespace}
  {any attribute not in default or any TT namespace}>
  Content: ({any element in TT Metadata namespace}|{any element not in any TT namespace})*
</metadata>

The use of document metadata is illustrated by the following example.

...
<head>
  <metadata xmlns:ttm="http://www.w3.org/ns/ttml#metadata">
    <ttm:title>Document Metadata Example</ttm:title>
    <ttm:desc>This document employs document metadata.</ttm:desc>
  </metadata>
</head>
...

The use of element metadata is illustrated by the following example.

...
<div>
  <metadata xmlns:ttm="http://www.w3.org/ns/ttml#metadata">
    <ttm:title>Chapter 6 – Sherlock Holmes Gives a Demonstration</ttm:title>
    <ttm:desc>Holmes shows Watson how the murderer entered the window.</ttm:desc>
  </metadata>
</div>
...

The use of metadata attribute items is illustrated by the following example.

...
<div xmlns:ext="http://example.org/ttml#metadata">
  <metadata ext:ednote="remove this division prior to publishing"/>
</div>
...

The use of foreign element metadata is illustrated by the following example.

...
<metadata
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:dcterms="http://purl.org/dc/terms/"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <dc:title>Foreign Element Metadata Example</dc:title>
  <dc:description>Express metadata using elements in foreign namespace.</dc:description>
  <dc:format xsi:type="dcterms:IMT">application/ttml+xml</dc:format>
</metadata>
...

12.1.2 ttm:title

The ttm:title element is used to express a human-readable title of a specific element instance.

<ttm:title
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: #PCDATA
</ttm:title>

Examples of the ttm:title element are shown above in Example Fragment – Document Metadata and Example Fragment – Element Metadata.

12.1.3 ttm:desc

The ttm:desc element is used to express a human-readable description of a specific element instance.

<ttm:desc
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: #PCDATA
</ttm:desc>

Examples of the ttm:desc element are shown above in Example Fragment – Document Metadata and Example Fragment – Element Metadata.

12.1.4 ttm:copyright

The ttm:copyright element is used to express a human-readable copyright that applies to some scoping level.

A copyright statement that applies to a document as a whole should appear as a child of the head element.

<ttm:copyright
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: #PCDATA
</ttm:copyright>

12.1.5 ttm:agent

The ttm:agent element is used to define an agent for the purpose of associating content information with an agent who is involved in the production or expression of that content.

The ttm:agent element accepts as its children zero or more ttm:name elements followed by zero or one ttm:actor element.

At least one ttm:name element child should be specified that expresses a name for the agent, whether it be the name of a person, character, group, or organization.

<ttm:agent
  type = (person|character|group|organization|other)
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: ttm:name*, ttm:actor?
</ttm:agent>

A type attribute must be specified on each ttm:agent element, and, if specified, must have one of the following values:

• person

• character

• group

• organization

• other

If the value of the type attribute is character, then the ttm:agent element instance should specify a ttm:actor child that specifies the agent that plays the role of the actor.

A ttm:agent metadata item is considered to be significant only when specified as a child of the head element or as a child of a metadata element child of the head element.

The use of agent metadata is illustrated by the following example.

<tt xml:lang="en" xmlns="http://www.w3.org/ns/ttml" xmlns:ttm="http://www.w3.org/ns/ttml#metadata">
  <head>
    <ttm:agent xml:id="connery" type="person">
      <ttm:name type="family">Connery</ttm:name>
      <ttm:name type="given">Thomas Sean</ttm:name>
      <ttm:name type="alias">Sean</ttm:name>
      <ttm:name type="full">Sir Thomas Sean Connery</ttm:name>
    </ttm:agent>
    <ttm:agent xml:id="bond" type="character">
      <ttm:name type="family">Bond</ttm:name>
      <ttm:name type="given">James</ttm:name>
      <ttm:name type="alias">007</ttm:name>
      <ttm:actor agent="connery"/>
    </ttm:agent>
  </head>
  <body>
    <div>
      ...  
      <p ttm:agent="bond">I travel, a sort of licensed troubleshooter.</p>
      ...  
    </div>
  </body>
</tt>

12.1.6 ttm:name

The ttm:name element is used to specify a name of a person, character, group, or organization.

<ttm:name
  type = (full|family|given|alias|other)
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: #PCDATA
</ttm:name>

A type attribute must be specified on each ttm:name element, and, if specified, must have one of the following values:

• full

• family

• given

• alias

• other

The relationship between the type of a name and the syntactic expression of the name is not defined by this specification.

Two examples of the ttm:name element are shown above in Example Fragment – Agent Metadata.

12.1.7 ttm:actor

The ttm:actor element is used to link the definition of a (role-based) character agent with another agent that portrays the character.

<ttm:actor
  agent = IDREF
  xml:id = ID
  xml:lang = string
  xml:space = (default|preserve)
  {any attribute not in default or any TT namespace}>
  Content: EMPTY
</ttm:actor>

The agent attribute of a ttm:actor element must reference a significant ttm:agent element that denotes the agent acting the part of a character.

An ttm:actor element referencing its parent ttm:agent element should be considered an error.

An example of the ttm:actor element is shown above in Example Fragment – Agent Metadata.

12.2.1 ttm:agent

The ttm:agent attribute takes an IDREFS value, and is used with certain Content elements to designate the agents that perform or are involved in the performance of the content.

If specified, a ttm:agent attribute must reference significant ttm:agent element instances.

The same IDREF, ID, should not appear more than once in the value of a ttm:agent attribute.

An example of the ttm:agent attribute is shown above in Example Fragment – Agent Metadata.

12.2.2 ttm:role

The ttm:role attribute may be used by a content author to express the roles, functions, or characteristics of some Content element that is so labeled.

If specified, the value of this attribute must adhere to the following syntax, where the syntactic element S must adhere to production [3] S as defined by [XML 1.0] § 2.3:

ttm:role
  role ( S role )*

role
  : "action"
  | "caption"
  | "description"
  | "dialog"
  | "expletive"
  | "kinesic"
  | "lyrics"
  | "music"
  | "narration"
  | "quality"
  | "sound"
  | "source"
  | "suppressed"
  | "reproduction"
  | "thought"
  | "title"
  | "transcription"
  | extension-role

extension-role
  : "x-" token-char+

token-char
  : { XML NameChar }    // XML 1.1 Production [4a]

The same role token, R, should not appear more than once in the value of a ttm:role attribute.