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# 2. The SMIL 2.0 Modules

Editors:
  Warner ten Kate (warner.ten.kate@philips.com), (Philips Electronics)
  Aaron Cohen (aaron.m.cohen@intel.com), (Intel)
  Philipp Hoschka (ph@w3.org), (W3C).

## Table of contents

## 2.1 Introduction

This section is informative.

Since the publication of SMIL 1.0 [SMIL10], interest in the integration of SMIL concepts with the HTML, the HyperText Markup Language [HTML4], and other XML languages, has grown. Likewise, the W3C HTML Working Group has specified XHTML, the Extensible HyperText Markup Language [XHTML10], in preparation to subset, extend, and integrate it with other languages. The strategy considered for integrating respective functionality with other XML-based languages is based on the concepts of modularization and profiling [SMIL-MOD], [XMOD].

Modularization is an approach in which markup functionality is specified as a set of modules that contain semantically-related XML elements, attributes, and attribute values. Profiling is the creation of an XML-based language through combining these modules, in order to provide the functionality required by a particular application.

Profiling introduces the ability to tailor an XML-based language to specific needs, e.g. to optimize presentation and interaction for the client's capabilities. Profiling also adds the ability for integrating functionality from other markup languages, releasing the language designer from specifying that functionality. Moreover, it provides for consistency in markup through the use of the same model to incorporate a function. Identical constructs ease authoring, while at the user agent side there is a potential for re-use of code. For example, a scheduler supporting SMIL timing and synchronization functionality could be used for SMIL documents, XHTML+SMIL documents, and SVG documents.

Modularization enables language designers to specify dedicated markup intended for integration with other, existing, language profiles. Examples of specifications intended for such integration are MathML and XForms [MathML], [XFORMS].

Modularization and profiling use the extensibility properties of XML, and related technology like XML namespaces and XML Schema [XML10], [XML-NS], [XSCHEMA].

This part of the SMIL 2.0 specification describes the framework on which SMIL modularization and profiling is based, and specifies the SMIL 2.0 Modules, their identifiers, and the requirements for conformance within this framework.

### 2.1.1 Modularization and Profiling

This section is informative.

The modularization approach used in this specification derives from that set forth in XHTML Modularization [XMOD]. The framework on which SMIL modularization and profiling is based, is informally described here.

A Module is a collection of semantically-related XML elements, attributes, and attribute values that represents a unit of functionality. Modules are defined in coherent sets. This coherency is expressed in that the elements of these modules are associated with the same namespace.

A Language Profile is a combination of modules. Modules are atomic, i.e. they cannot be subset when included in a language profile. Furthermore, a module specification may include a set of integration requirements, to which language profiles that include the module must comply.

Commonly, there is a main language profile that incorporates nearly all the modules associated with a single namespace. For example, the SMIL 2.0 language profile uses most of the SMIL 2.0 modules. Usually, the same name is used to loosely reference both - "SMIL 2.0" in the example. Also, the name "profile" is used to mean "language profile".

Other language profiles can be specified that are subsets of the larger one, or that incorporate a mixture of modules associated with different namespaces. SMIL 2.0 Basic is an example of the first, XHTML+SMIL of the latter.

A special module in a language profile is the so-called Structure Module, in that it contains the root element of the language profile, e.g. <smil> or <html>. Any language profile that incorporates modules associated with a single namespace will include the Structure module associated with that namespace.

Other modules that require special mention are those that characterize the core of the functionality provided by the namespace. This is expressed by the notions of host language and integration set. Both of them relate to a set of conformance requirements for language profiles, which includes the requirement to incorporate at least the core set of modules. The set may be different for a host language and an integration set. A host language must incorporate the Structure module; an integration set need not. There may be other differences as well.

The main purpose of language profile conformance is to enhance interoperability. Preferably, the mandatory modules for host language conformance are defined in such a way that any document interchanged in a conforming language profile will yield a reasonable presentation when the document renderer, while supporting the associated mandatory module set, would ignore all other (unknown) elements and attributes. Here, "reasonable presentation" is to be understood as something intelligible, which is not necessarily a close reflection of the author's original intentions. To achieve the latter, a negotiation would have to be conducted to agree on the specific language profile to be used for the document interchange.

## 2.2 SMIL 2.0 Modules

This section is normative.

SMIL functionality is partitioned into ten functional areas. Within each functional area a further partitioning is applied into modules. All of these modules, and only these modules, are associated with the SMIL namespace.

The functional areas and their corresponding modules are:

1. Timing
   1. AccessKeyTiming
   2. BasicInlineTiming
   3. BasicTimeContainers
   4. EventTiming
   5. ExclTimeContainers
   6. FillDefault
   7. MediaMarkerTiming
   8. MinMaxTiming
   9. MultiArcTiming
   10. RepeatTiming
   11. RepeatValueTiming
   12. RestartDefault
   13. RestartTiming
   14. SyncbaseTiming
   15. SyncBehavior
   16. SyncBehaviorDefault
   17. SyncMaster
   18. TimeContainerAttributes
   19. WallclockTiming
2. Time Manipulations
   1. TimeManipulations
3. Animation
   1. BasicAnimation
   2. SplineAnimation
4. Content Control
   1. BasicContentControl
   2. CustomTestAttributes
   3. PrefetchControl
   4. SkipContentControl
5. Layout
   1. AudioLayout
   2. BasicLayout
   3. HierarchicalLayout
   4. MultiWindowLayout
6. Linking
   1. BasicLinking
   2. LinkingAttributes
   3. ObjectLinking
7. Media Objects
   1. BasicMedia
   2. BrushMedia
   3. MediaAccessibility
   4. MediaClipping
   5. MediaClipMarkers
   6. MediaDescription
   7. MediaParam
8. Metainformation
   1. Metainformation
9. Structure
   1. Structure
10. Transitions
    1. BasicTransitions
    2. InlineTransitions
    3. TransitionModifiers

This section is informative.

Each of these modules introduces a set of semantically-related elements, properties, and attributes. Each functional area has a corresponding section in this specification document. Further details on each of the modules is specified within those sections.

The modules may be independent or complementary. For example, the SyncMaster module requires and builds upon the SyncBehavior module, but the PrefetchControl and SkipContentControl modules are independent from each other. In addition, some modules require modules from other functional areas.

Modules specify their integration requirements. When one module requires another module for basic features and as a prerequisite for integration, a language profile must include the second module in order to include the first. The first module is said to be a dependent of the second module. Dependency may be nested, in that a module may be dependent on a module that is dependent itself.

Table 1 presents the SMIL 2.0 modules and the modules they dependent on.

Table 1: The SMIL 2.0 Modules and their Dependencies.
Module | Dependencies
AccessKeyTiming | NONE
AudioLayout | BasicLayout
BasicAnimation | BasicInlineTiming
BasicContentControl | NONE
BasicInlineTiming | NONE
BasicLayout | NONE
BasicLinking | NONE
BasicMedia | NONE
BasicTimeContainers | NONE
BasicTransitions | NONE
BrushMedia | NONE
CustomTestAttributes | BasicContentControl
EventTiming | NONE
ExclTimeContainers | NONE
FillDefault | BasicTimeContainers, and/or ExclTimeContainers, and/or TimeContainerAttributes
HierarchicalLayout | BasicLayout
InlineTransitions | NONE
LinkingAttributes | NONE
MediaAccessibility | MediaDescription
MediaClipMarkers | MediaClipping
MediaClipping | BasicMedia
MediaDescription | NONE
MediaMarkerTiming | NONE
MediaParam | BasicMedia
MetaInformation | NONE
MinMaxTiming | NONE
MultiArcTiming | AccessKeyTiming, and/or BasicInlineTiming, and/or EventTiming, and/or MediaMarkerTiming, and/or RepeatValueTiming, and/or SyncbaseTiming, and/or WallclockTiming
MultiWindowLayout | BasicLayout
ObjectLinking | BasicLinking
PrefetchControl | NONE
RepeatTiming | NONE
RepeatValueTiming | NONE
RestartDefault | RestartTiming
RestartTiming | NONE
SkipContentControl | NONE
SplineAnimation | BasicAnimation
Structure | BasicContentControl, and BasicInlineTiming, and BasicLayout, and BasicLinking, and BasicMedia, and BasicTimeContainers, and SkipContentControl, and SyncbaseTiming
SyncbaseTiming | NONE
SyncBehavior | BasicTimeContainers, and/or ExclTimeContainers, and/or TimeContainerAttributes
SyncBehaviorDefault | SyncBehavior
SyncMaster | SyncBehavior
TimeContainerAttributes | NONE
TimeManipulations | NONE
TransitionModifiers | BasicTransitions, and/or InlineTransitions
WallclockTiming | NONE

### 2.2.1 SMIL DOM

This section is informative.

SMIL is an XML-based language and conforms to the (XML) DOM Core [DOM1], [DOM2]. In the future, a SMIL-specific DOM recommendation may specify support for timing and synchronization, media integration, and other synchronized multimedia functionality.

A language profile may include DOM support. The granularity of DOM being supported corresponds to the modules being selected in that language profile. As with all modules, required support for the DOM is an option of the language profile.

## 2.3 Identifiers for SMIL 2.0 Modules and Language Profiles

This section is informative.

This section specifies the identifiers for the SMIL 2.0 namespace and the SMIL 2.0 modules. Each SMIL host language conformant language profile is requested to explicitly state the namespace URI that is to be used to identify it. That namespace URI must comply with the "Requirements on Identifiers for SMIL Host Language Conformant Language Profiles", defined below.

### 2.3.1 The SMIL Mime Type

This section is normative.

Documents authored in language profiles that include the SMIL Structure module can be associated with the "application/smil" mime type. Documents using the "`application/smil`" mime type are required to be host language conformant.

### 2.3.2 XML Namespace Identifier for the SMIL 2.0 Modules

This section is normative.

The XML namespace identifier for the complete set of SMIL 2.0 modules, and the elements and attributes that are contained within is:

`http://www.w3.org/2001/SMIL20/`

### 2.3.3 Identifiers for SMIL 2.0 Modules and Features

This section is normative.

Each module in this specification has a unique identifier associated with it. They are intended to uniquely and consistently identify each of them. They should be used as values in a test for whether an implementation includes a specific module, as well as in other circumstances where a need to refer to a specific SMIL 2.0 module is necessary.

Table 2 summarizes the identifiers for SMIL 2.0 modules.

Table 2: The SMIL 2.0 Module Identifiers.
Module name | Identifier
AccessKeyTiming | `http://www.w3.org/2001/SMIL20/AccessKeyTiming`
AudioLayout | `http://www.w3.org/2001/SMIL20/AudioLayout`
BasicAnimation | `http://www.w3.org/2001/SMIL20/BasicAnimation`
BasicContentControl | `http://www.w3.org/2001/SMIL20/BasicContentControl`
BasicInlineTiming | `http://www.w3.org/2001/SMIL20/BasicInlineTiming`
BasicLayout | `http://www.w3.org/2001/SMIL20/BasicLayout`
BasicLinking | `http://www.w3.org/2001/SMIL20/BasicLinking`
BasicMedia | `http://www.w3.org/2001/SMIL20/BasicMedia`
BasicTimeContainers | `http://www.w3.org/2001/SMIL20/BasicTimeContainers`
BasicTransitions | `http://www.w3.org/2001/SMIL20/BasicTransitions`
BrushMedia | `http://www.w3.org/2001/SMIL20/BrushMedia`
CustomTestAttributes | `http://www.w3.org/2001/SMIL20/CustomTestAttributes`
EventTiming | `http://www.w3.org/2001/SMIL20/EventTiming`
ExclTimeContainers | `http://www.w3.org/2001/SMIL20/ExclTimeContainers`
FillDefault | `http://www.w3.org/2001/SMIL20/FillDefault`
HierarchicalLayout | `http://www.w3.org/2001/SMIL20/HierarchicalLayout`
InlineTransitions | `http://www.w3.org/2001/SMIL20/InlineTransitions`
LinkingAttributes | `http://www.w3.org/2001/SMIL20/LinkingAttributes`
MediaAccessibility | `http://www.w3.org/2001/SMIL20/MediaAccessibility`
MediaClipMarkers | `http://www.w3.org/2001/SMIL20/MediaClipMarkers`
MediaClipping | `http://www.w3.org/2001/SMIL20/MediaClipping`
MediaDescription | `http://www.w3.org/2001/SMIL20/MediaDescription`
MediaMarkerTiming | `http://www.w3.org/2001/SMIL20/MediaMarkerTiming`
MediaParam | `http://www.w3.org/2001/SMIL20/MediaParam`
Metainformation | `http://www.w3.org/2001/SMIL20/Metainformation`
MinMaxTiming | `http://www.w3.org/2001/SMIL20/MinMaxTiming`
MultiArcTiming | `http://www.w3.org/2001/SMIL20/MultiArcTiming`
MultiWindowLayout | `http://www.w3.org/2001/SMIL20/MultiWindowLayout`
ObjectLinking | `http://www.w3.org/2001/SMIL20/ObjectLinking`
PrefetchControl | `http://www.w3.org/2001/SMIL20/PrefetchControl`
RepeatTiming | `http://www.w3.org/2001/SMIL20/RepeatTiming`
RepeatValueTiming | `http://www.w3.org/2001/SMIL20/RepeatValueTiming`
RestartDefault | `http://www.w3.org/2001/SMIL20/RestartDefault`
RestartTiming | `http://www.w3.org/2001/SMIL20/RestartTiming`
SkipContentControl | `http://www.w3.org/2001/SMIL20/SkipContentControl`
SplineAnimation | `http://www.w3.org/2001/SMIL20/SplineAnimation`
Structure | `http://www.w3.org/2001/SMIL20/Structure`
SyncbaseTiming | `http://www.w3.org/2001/SMIL20/SyncbaseTiming`
SyncBehavior | `http://www.w3.org/2001/SMIL20/SyncBehavior`
SyncBehaviorDefault | `http://www.w3.org/2001/SMIL20/SyncBehaviorDefault`
SyncMaster | `http://www.w3.org/2001/SMIL20/SyncMaster`
TimeContainerAttributes | `http://www.w3.org/2001/SMIL20/TimeContainerAttributes`
TimeManipulations | `http://www.w3.org/2001/SMIL20/TimeManipulations`
TransitionModifiers | `http://www.w3.org/2001/SMIL20/TransitionModifiers`
WallclockTiming | `http://www.w3.org/2001/SMIL20/WallclockTiming`

In addition to the module identifiers above, there may be different features and variances from one language profile to another that may not be expressed as the support or non-support of a particular module. These features may be expressed using the following identifiers:

`http://www.w3.org/2001/SMIL20/NestedTimeContainers`
  Profile allows nesting of the par and seq time containers.
`http://www.w3.org/2001/SMIL20/DeprecatedFeatures`
  Profile supports deprecated SMIL 1.0 features.

Implementations that support the SMIL BasicContentControl module must allow these as identifiers for use with the XML namespace mechanism, and must allow the associated namespace identifier to be used with the systemRequired test attribute. Profiles must identify those attributes for which an implementation must return "true" (this is an integration requirement). Implementations must return "false" for modules or features which are not fully supported.

Modules can also be identified collectively. The following four module collections are defined:

`http://www.w3.org/2001/SMIL20/`
  All the modules specified by the SMIL 2.0 specification.
`http://www.w3.org/2001/SMIL20/Language`
  The modules used by the SMIL 2.0 Language profile.
`http://www.w3.org/2001/SMIL20/HostLanguage`
  The modules required for SMIL Host Language Conformance.
`http://www.w3.org/2001/SMIL20/IntegrationSet`
  The modules required for SMIL Integration Set Conformance.

## 2.4 SMIL Conformance

This section is informative.

In this section we specify the rules for SMIL host language and SMIL integration set conformance. First, the conformance requirements for host language conformance and integration set conformance are given. The requirements are similar to those set forth for XHTML host language document type conformance and XHTML integration set document type conformance [XMOD]. In a final section the requirements on identifiers for host language conformant language profiles are given.

Currently, there exist three language profiles using SMIL 2.0 Modules. They are the SMIL 2.0 Language Profile, the SMIL 2.0 Basic Language Profile, and the XHTML+SMIL 2.0 Language Profile [XHTML+SMIL]. The first two are SMIL host language conformant, the third is SMIL integration set conformant.

This section is normative.

The following two tables list names used to collectively reference certain sets of SMIL 2.0 elements and attributes. These are used in the definitions of the minimum support in the two sections below on SMIL host language conformance and SMIL integration set conformance. The term "minimum support" is used to refer to the minimum set of elements that an element can contain, and the minimum set of attributes that can be used on an element.

Table 3: Names of SMIL 2.0 Element Collections.
Element Set Name | Elements
TIMING-ELMS | par, seq
MEDIA-ELMS | ref, animation, audio, img, video, text, textstream
EMPTY | no elements are required as a minimum

Table 4: Names of SMIL 2.0 Attribute Collections.
Attribute Set Name | Attributes
TIMING-ATTRS | begin, end, dur, repeatDur, repeatCount, max, min, fill, endsync
CONTCTRL-ATTRS | systemBitrate, systemCaptions, systemLanguage, systemRequired, systemScreenSize, systemScreenDepth, systemOverdubOrSubtitle, systemAudioDesc, systemOperatingSystem, systemCPU, systemComponent
MEDIA-ATTRS | src, type
LINKING-ATTRS | href, sourceLevel, destinationLevel, sourcePlaystate, destinationPlaystate, show, accesskey, tabindex, target, external, actuate, alt
COMMON-ATTRS | id, class, xml:lang, title

### 2.4.1 SMIL Host Language Conformance

This section is normative.

A language profile is said to be SMIL 2.0 host language conformant if it includes the following modules:

1. Structure
2. BasicContentControl
3. BasicInlineTiming
4. BasicLayout
5. BasicLinking
6. BasicMedia
7. BasicTimeContainers
8. MinMaxTiming
9. RepeatTiming
10. SkipContentControl
11. SyncbaseTiming

In addition, the following requirements must be satisfied:

1. The language profile defines what modules it collects.
2. The language profile includes all elements, attributes, and attribute values specified by the collected modules.
3. The language profile fulfills the "minimum support" requirements for elements and attributes as listed in Table 5 below.
4. The language profile complies with the integration requirements set forth by the modules it collects.
5. The language profile specifies the semantics related to the integration of the modules.
6. The language profile defines its DTD or XML Schema.
7. The language profile defines a unique identifier conforming to the requirements set forth in Requirements on Identifiers for SMIL Host Language Conformant Language Profiles.
8. The SyncbaseTiming module should be included in Host Language conformant profiles, although it is not strictly required. We strongly recommend inclusion of this module in Host Language conformant profiles to maintain a high level of consistency and interoperability with other languages that have integrated SMIL modules including the SMIL 2.0 Language, XHTML+SMIL, and SVG. Only profiles designed to operate on severely constrained devices may omit the SyncbaseTiming module.

Table 5: Minimum Support for SMIL Host Language Conformance.
Element | Minimum Support
Elements | Attributes
smil | head, body | COMMON-ATTRS, CONTCTRL-ATTRS, xmlns
head | layout, switch | COMMON-ATTRS
body | TIMING-ELMS, MEDIA-ELMS, switch, a | COMMON-ATTRS
layout | root-layout, region | COMMON-ATTRS, CONTCTRL-ATTRS, type
root-layout | EMPTY | COMMON-ATTRS, backgroundColor, height, width, skip-content
region | EMPTY | COMMON-ATTRS, backgroundColor, bottom, fit, height, left, right, showBackground, top, width, z-index, skip-content, regionName
ref, animation, audio, img, video, text, textstream | area | COMMON-ATTRS, CONTCTRL-ATTRS, TIMING-ATTRS, repeat, MEDIA-ATTRS, region
a | MEDIA-ELMS | COMMON-ATTRS, LINKING-ATTRS
area | EMPTY | COMMON-ATTRS, LINKING-ATTRS, TIMING-ATTRS, repeat, shape, coords, nohref
par, seq | TIMING-ELMS, MEDIA-ELMS, switch, a | COMMON-ATTRS, CONTCTRL-ATTRS, TIMING-ATTRS, repeat
switch | TIMING-ELMS, MEDIA-ELMS, a, layout | COMMON-ATTRS, CONTCTRL-ATTRS

Support of deprecated elements and attributes is required for SMIL 2.0 host language conformance for all modules the given language supports. For example, if a SMIL 2.0 host language supports the MultiArcTiming module, it must support the deprecated syntax defined in the MultiArcTiming module.

Since the SMIL 2.0 Structure module may only be used in a profile that is SMIL host language conformant, this implies that the SMIL 2.0 Structure module must at least be accompanied with the nine other modules required for host language conformance that were named above. Those modules themselves can still be used in other, non SMIL host language conformant, language profiles.

### 2.4.2 SMIL Integration Set Conformance

This section is normative.

A language profile is said to be SMIL 2.0 integration set conformant if it includes the following modules:

1. BasicContentControl
2. BasicInlineTiming
3. BasicMedia
4. BasicTimeContainers
5. MinMaxTiming
6. RepeatTiming
7. SyncbaseTiming

In addition, the following requirements must be satisfied:

1. The language profile defines what modules it collects.
2. The language profile includes all elements, attributes, and attribute values specified by the collected SMIL 2.0 modules.
3. The language profile fulfills the "minimum support" requirements for elements and attributes as listed in Table 6 below.
4. The language profile complies with the integration requirements set forth by the SMIL 2.0 modules it collects.
5. The SyncbaseTiming module should be included in Integration Set conformant profiles, although it is not strictly required. We strongly recommend inclusion of this module in Integration Set conformant profiles to maintain a high level of consistency and interoperability with other languages that have integrated SMIL modules including the SMIL 2.0 Language, XHTML+SMIL [XHTML+SMIL], and SVG [SVG]. Only profiles designed to operate on severely constrained devices may omit the SyncbaseTiming module.

Table 6: Minimum Support for SMIL Integration Set Conformance.
Element | Minimum Support
Elements | Attributes
ref, animation, audio, img, video, text, textstream |  | CONTCTRL-ATTRS, TIMING-ATTRS, MEDIA-ATTRS
par, seq | TIMING-ELMS, MEDIA-ELMS, switch, a | CONTCTRL-ATTRS, TIMING-ATTRS
switch | TIMING-ELMS, MEDIA-ELMS | CONTCTRL-ATTRS

Support of deprecated elements and attributes is not required for SMIL 2.0 integration set conformance. However, when included, the above requirements also apply to these elements and attributes. Also, when supported, it is required that all the deprecated elements and attributes from all the included modules are supported as a whole.

### 2.4.3 Requirements on Identifiers for SMIL Host Language Conformant Language Profiles

This section is informative.

A language profile is specified through its DTD or XML Schema. The identifier of these can be used to identify the language profile. SMIL 1.0 has specified the default namespace declaration on its root element, smil, as the decisive identifier for distinguishing it from other language profiles [SMIL10]. For that purpose SMIL 1.0 has specified

`http://www.w3.org/TR/REC-smil`

as the namespace identifier for SMIL 1.0.

This section is normative.

For the purpose of identifying the version and the language profile used, SMIL host language conformant documents must satisfy the following requirements:

1. The document should declare a default namespace [XML-NS].
2. The default namespace must be declared on the smil root element.
3. In case the SMIL host language conformant language profile has been issued as a W3C Recommendation, the default namespace identifier must satisfy the following requirements:
   1. The URI is constructed conformant to the requirements set forth by the W3C [W3C-NSURI].
   2. The default namespace identifier should identify the language profile.
      In case the language profile is a subset of a larger one, the default namespace identifier may also identify that larger language profile. The module collection that is required to be supported in the subset language profile may be indicated through the systemRequired attribute on the smil element.
      See the SMIL Basic Language Profile specification for an example.

### 2.4.4 Error Handling in SMIL Host Language Conformant Documents

This section is normative.

Syntax errors in a SMIL Host Language conformant document are handled according to the XML rules for well-formed or valid XML [XML10].

Semantic errors can arise at various levels. One is where the declared attribute values are of unknown value. Another is where the assembled presentation is (possibly) conflicting, as in a case where media objects are competing for display space or where they are synchronized ambiguously. These latter types, although maybe an error according to the author's intentions, are not considered an error and the user agent will present according to the resolution rules defined in this specification.

### 2.4.5 Handling of Syntax errors in Attribute Values

This section is normative.

Errors in attribute values might remain undetectable to the parser, because the value type is declared as CDATA, or because the value range is open ended, as in the case of events, for example. However, errors in attribute values can be detected within a given language profile, where that language profile specifies the supported value set. Specifications of language profiles are required to specify the error handling that is required when such an attribute value error occurs.

## 2.5 Creating a DTD for a Language Profile

This section is informative.

This section describes how language profiles could be defined using the SMIL 2.0 modular DTDs. The reader is assumed to be familiar with the mechanisms defined in "Modularization of XHTML" [XMOD], in particular Appendix D [XMOD-APPD] and Appendix E [XMOD-APPE]. In general, the SMIL 2.0 modular DTDs use the same mechanisms as the XHTML modular DTDs use. Exceptions to this are:

1. SMIL supports qualified attribute names for SMIL attributes that can appear on non-SMIL elements. This enables these attributes to use prefixes to indicate that they belong to the SMIL 2.0 namespace.
2. SMIL supports module level INCLUDE/IGNORE instead of XHTML's element/attlist level. Similar to XHTML Modularization, this prohibits profiles from importing only part of a module -- they have to support either all the elements and attributes or none.

Below, we give a short description of the files that are used to define the SMIL 2.0 modular DTDs. See the table and the end of the section for a complete list of the filenames involved.

Following the same mechanisms as the XHTML modular DTDs, the SMIL 2.0 specification places the XML element declarations (e.g. <!ELEMENT...>) and attribute list declarations (e.g. <!ATTLIST...>) of all SMIL 2.0 elements in separate files, the SMIL module files. A SMIL module file is provided for each functional area in the SMIL 2.0 specification (that is, there is a SMIL module file for animation, layout, timing, etc).

The SMIL module files are used in the normative definitions of the specification of the SMIL 2.0 Language Profile. Usage of the same module files for defining other SMIL profiles is recommended, but not required. The requirements that SMIL language profiles must follow are stated in the SMIL 2.0 specification, not in the DTD code.

To make the SMIL module files independent of each other, and independent of the language profiles, the element and attribute declarations make heavy use of XML entities. This provides profiles with the necessary hooks to define the actual content models and attributes of the SMIL elements.

The SMIL 2.0 Language Profile provides examples of how the SMIL module files can be used. Most of the DTD files are reused across the different profiles. Reused are the SMIL module files, the files that define the data types and the common attributes, the "qname" file that takes care of adding namespace prefixes if necessary, and the framework file, which takes care of including files in the appropriate order.

The files that are different for each profile are the driver file and document model file. This would, in general, also apply to new profiles: to define a new language profile, one has to write the extension module(s), the driver file that defines which modules are used, and a document model file that defines the extended document model. The driver file and document model file are described in more detail below.

The driver file.

This is the file that would be referenced by a document's DOCTYPE declaration. Its main job is to define which document model file and which of the SMIL module files the profile is using. It may also define an optional namespace to be used in all namespace prefixes. For example, to prefix all SMIL element names with "foobar", the following can be added to the start of the profile:

`<!ENTITY % SMIL.prefixed "INCLUDE" >
<!ENTITY % SMIL.prefix "foobar" >`

Elements defined in their modules as, for example, <video> will become parsed as <foobar:video>. This also applies for SMIL attributes that appear on other elements, so, for example, "begin" becomes "foobar:begin". The default is that the qname prefix is empty -- that is, it is effectively turned off by default.

After these definitions, the driver file includes the framework file (which will subsequently include the data type, common attributes, qname and document model file), after which the SMIL module files are included that are used by this profile.

The document model file.

The document model file contains the XML entities that are used by the SMIL module files to define the content models and attribute lists of the elements in that profile.

Content models generally differ from profile to profile, or contain elements from other modules. To avoid these dependencies in the SMIL module files, content models need to be defined in the document model file. The (dummy) default content model as defined in the SMIL module files is "EMPTY" for all SMIL 2.0 elements.

For the same reasons, the SMIL module files only define a default attribute list for their elements. This default list only contains the SMIL 2.0 core attributes and the attributes that are defined in the same SMIL module file. All other attributes need to be added to this default list by defining the appropriate XML entities. For example, the Media Objects Module file only adds the core and media related attributes on the media objects; other attributes, such as the timing attributes, are added to this list by the document model file.

Table 7: Formal public identifiers and system identifiers of all files used in the SMIL 2.0 modular DTDs.
Driver files for the predefined profiles
-//W3C//DTD SMIL 2.0//EN | `http://www.w3.org/2001/SMIL20/SMIL20.dtd`

Document model files for the predefined profiles
-//W3C//ENTITIES SMIL 2.0 Document Model 1.0//EN | `http://www.w3.org/2001/SMIL20/smil-model-1.mod`

SMIL 2.0 module files
-//W3C//ELEMENTS SMIL 2.0 Animation//EN | `http://www.w3.org/2001/SMIL20/SMIL-anim.mod`
-//W3C//ELEMENTS SMIL 2.0 Content Control//EN | `http://www.w3.org/2001/SMIL20/SMIL-control.mod`
-//W3C//ELEMENTS SMIL 2.0 Layout//EN | `http://www.w3.org/2001/SMIL20/SMIL-layout.mod`
-//W3C//ELEMENTS SMIL 2.0 Linking//EN | `http://www.w3.org/2001/SMIL20/SMIL-link.mod`
-//W3C//ELEMENTS SMIL 2.0 Media Objects//EN | `http://www.w3.org/2001/SMIL20/SMIL-media.mod`
-//W3C//ELEMENTS SMIL 2.0 Document Metainformation//EN | `http://www.w3.org/2001/SMIL20/SMIL-metainformation.mod`
-//W3C//ELEMENTS SMIL 2.0 Document Structure//EN | `http://www.w3.org/2001/SMIL20/SMIL-struct.mod`
-//W3C//ELEMENTS SMIL 2.0 Timing//EN | `http://www.w3.org/2001/SMIL20/SMIL-timing.mod`
-//W3C//ELEMENTS SMIL 2.0 Transition//EN | `http://www.w3.org/2001/SMIL20/SMIL-transition.mod`

Other utilities: data types, common attributes, qname and frame work files
-//W3C//ENTITIES SMIL 2.0 Datatypes 1.0//EN | `http://www.w3.org/2001/SMIL20/smil-datatypes-1.mod`
-//W3C//ENTITIES SMIL 2.0 Common Attributes 1.0//EN | `http://www.w3.org/2001/SMIL20/smil-attribs-1.mod`
-//W3C//ENTITIES SMIL 2.0 Qualified Names 1.0//EN | `http://www.w3.org/2001/SMIL20/smil-qname-1.mod`
-//W3C//ENTITIES SMIL 2.0 Modular Framework 1.0//EN | `http://www.w3.org/2001/SMIL20/smil-framework-1.mod`

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