16. SMIL 3.0 Scalability Framework

This section is normative.

SMIL 3.0 provides a scalability framework, where a family of scalable SMIL profiles can be defined using a sub- or superset of the SMIL 3.0 Language, Daisy, Mobile, or Extended Mobile profiles, or a superset of the SMIL 3.0 Tiny profile. A SMIL document can be authored conforming to the scalability framework such that it provides limited functionality on a resource-constrained device while allowing richer capabilities on a more capable device. This section defines the requirements for conforming SMIL documents and SMIL user agents. Moreover, it describes scalable SMIL profile architecture, guidelines for defining them, and their conformance requirements.

This section is normative.

A scalable profile is defined by extending any SMIL host language conforming profile using the content control facilities to support application/device specific features via a namespace mechanism. Individual user agents may opt-out of a particular language feature by explicitly ignoring it during document processing. In this way, both author and user-agent-development needs are supported for a wide community without have to define a large number of standard profiles.

In SMIL 3.0, the scalability framework can also be applied between two host language profiles where one language is made of a strict subset of the modules of the other language. This is the scalability to profiles framework. The scalability to profiles framework allows, for example, the definition of a base line profile and a more advanced profile. It also allows constraining the modules used in the scalability of the base line profile to those of the advanced profile. In this case, the base line profile is said to be a scalable profile to the more advanced profile.

A scalable profile to a profile is defined by extending its set of modules using the content control facilities to support application/device specific features via a namespace mechanism. The scalable profile to a given profile must include the description of the language it scales to, for example by including a description of its namespace.

16.4.1 Conforming SMIL 3.0 Documents

A SMIL 3.0 document is a conforming SMIL 3.0 document if it adheres to the specification of the corresponding SMIL profile definition, including SMIL 3.0's DTD (see Document Type Definition). A conforming SMIL 3.0 document must meet all of the following criteria:

1. The root element of the document must be the smil element.
2. The document must be well-formed XML.
3. It must conform to the following W3C Recommendations:
   • The XML 1.1 specification (Extensible Markup Language (XML) 1.1) [XML11].
   • Namespaces in XML [XML-NS]. Full XML Namespaces must be supported.
   • Any use of CSS styles and properties shall conform to Cascading Style Sheets, level 2 CSS2 Specification [CSS2].
4. A SMIL 3.0 document may contain the DOCTYPE declaration defined within the relevant profile specification. If a document contains this declaration, it must be a valid XML document. Note that this implies that extensions to the syntax defined in the DTD are not allowed. If the document is invalid, the user agent should issue an error.

   A document is a conforming SMIL 3.0 document if it satisfies the requirements of the relevant profile specification and is valid per the normative DTD identified by that profile.

   Per section 7.6 of the W3C Process Document, W3C will make every effort to make this normative DTD available in its original form at this URI.

   The SYMM WG also publishes a non-normative SMIL 3.0 DTD identified by

   http://www.w3.org/2007/07/SMIL30/SMIL30.dtd
   

   The SYMM WG plans to make changes to this DTD over time to correct errata. If you choose to refer to this DTD, please note that it is subject to change without notice at any time. The SYMM WG MAY publish a normative "snapshot" of the corrected DTD at a new URI by following the W3C Process for modifying a Recommendation.

   Individuals are free to use either of the two URIs above as the system identifier in the SMIL 3.0 profile's DOCTYPE, according to the desired level of stability.

5. A document must declare a default namespace for its elements with an xmlns attribute on the smil root element. The default namespace declaration must be defined by the relevant profile specification. The default namespace URI may only be used to refer to the approved version of profile's specification: different URIs will be used for any and all new versions of the profile. The default namespace name may be reused in any update of the profile which is made for the purpose of clarification or bug fixes. These changes will be minor in that they do not (a) change the meaning of existing documents written using the namespace, or (b) affect the operation of existing software written to process such documents. The SYMM WG may reuse this namespace URI in a future specification that revises the SMIL 3.0 DTD, thus affecting the validity of published documents.
6. A document may declare both an XML DOCTYPE declaration (as defined in [XML11]) and one or more XML namespace declarations (as defined in [XML-NS]). To be recognized as a SMIL 3.0 document by a conforming SMIL 3.0 user agent, the document must include the SMIL 3.0 namespace identifier as the default namespace on the <smil> tag. For example:

   Declare a SMIL 3.0 document with custom extensions conforming to a custom DTD:

   <!DOCTYPE smil SYSTEM "http://www.example.org/myveryownSMIL.dtd">
   <smil xmlns="http://www.w3.org/ns/SMIL" version="3.0" baseProfile="Language"
           xmlns:mysmil="http://www.example.org/2005/SMIL30/Language">
           <mysmil:foo>
           ...
           </mysmil:foo>
   </smil>

7. A document that declares neither a DOCTYPE nor a default namespace declaration will be processed as a SMIL 1.0 document. Extension elements or attributes not defined by the SMIL 1.0 namespace should be declared using the XML namespace mechanism.
8. Given that, as of this writing, DTDs have no way to describe the allowability of namespace-qualified extensions, and that extensions to SMIL 3.0 conformant documents must be namespace-qualified, here is the algorithm to be used to validate documents with extensions:

   If all non-SMIL 3.0 namespace elements and attributes and all xmlns attributes which refer to non-SMIL 3.0 namespace elements are removed from the given document and if the appropriate <!DOCTYPE ... > statement which points to the SMIL 3.0 DTD is included, the result is a valid XML document.

9. Many SMIL 3.0 attributes are associated with several SMIL 3.0 and SMIL 2.0 namespaces including the module namespaces, module collection namespaces, the SMIL 3.0 language namespace, and the overall SMIL 3.0 namespace. Attributes in the SMIL 3.0 namespaces having the same local part are considered the same attribute as far as SMIL 3.0 Language document syntax. It is illegal to use a SMIL 3.0 attribute several times on an element, even if each occurrence is qualified by a different SMIL 3.0 namespace, and SMIL user agents shall treat this as a syntax error. For example, the following document fragment is an error, because the begin attribute appears twice on the ref element:

   <smil xmlns="http://www.w3.org/ns/SMIL" version="3.0" baseProfile="Language"
           xmlns:BasicInlineTiming="http://www.w3.org/2007/07/SMIL30/BasicInlineTiming">
   ...
   <ref begin="5s" BasicInlineTiming:begin="5s"/>
   ...
   </smil>

Neither the SMIL 3.0 definition nor these conformance criteria provide designated size limits on any aspect of SMIL 3.0 content. There are no maximum values on the number of elements, the amount of character data, or the number of characters in attribute values.

SMIL 3.0 deprecates base as a property value for the content attribute of the meta element of SMIL 1.0 in favor of the more general XML Base URI mechanisms.

All SMIL 3.0 profile specifications support the XML Base Recommendation [XMLBase]. XML Base is supported on all elements, and affects the interpretation of URIs as specified in the individual modules defining the URI attributes. Specifically, any applicable XML Base base URI must be applied to the interpretation of the href attribute of the link elements a, area and anchor, as well as the src attribute of the media elements audio, video, img, animation, textstream, text, and ref. XML Base must also be applied on longdesc and label attributes of all of the SMIL 3.0 elements.

The rules above should be revised once a normative XML Schema for SMIL 3.0 is available. This revision will take into account XML Schema validation.

16.4.2 Conforming SMIL 3.0 Language User Agents

A SMIL 3.0 user agent is a program which can parse and process a SMIL 3.0 document and render the contents of the document onto output media. A conforming SMIL 3.0 user agent must meet all of the following criteria:

1. In order to be consistent with the XML 1.1 Recommendation [XML11], the user agent must parse and evaluate a SMIL 3.0 document for well-formedness. If the user agent claims to be a validating user agent, it must also validate documents against their referenced DTDs according to [XML11].
2. When the user agent claims to support the functionality of SMIL 3.0 through SMIL 3.0 elements and attributes and the semantics associated with these elements and attributes, it must do so in ways consistent with this specification.
3. The user agent must be able to successfully parse and process any conforming SMIL 3.0 documents, and support and correctly implement the semantics of all features of the relevant SMIL 3.0 profile.
4. The XML parser of the user agent must be able to parse and process XML constructs defined in [XML11] and [XML-NS].
5. The default namespace on the smil root element recognized by the user agent will fall into one of three types:
   1. Default namespace on the smil root element recognized in its entirety by the user agent. The user agent should process the document as the version identified by the recognized namespace. Any elements, attributes, or other syntax not defined by the default namespace on the smil root element must be fully namespace qualified using the standard XML mechanisms for declaring namespaces for elements and attributes described in [XML-NS]. The "skip-content" mechanism (defined in the SkipContent module) will be applied to extension elements unrecognized by the user agent. Unqualified elements not part of the default namespace are illegal and must result in an error.

      Examples:

      1) A pure SMIL 1.0 document:

      <smil xmlns="http://www.w3.org/TR/REC-smil">
       ...
      </smil>  

      2) A pure SMIL 3.0 Language profile document:

      <smil xmlns="http://www.w3.org/ns/SMIL" version="3.0" baseProfile="Language">
       ...
      </smil>  

      3) A SMIL 1.0 document that has been extended to use the excl element:

      <smil xmlns="http://www.w3.org/TR/REC-smil"
            xmlns:smil30="http://www.w3.org/2007/07/SMIL30/" >
         <smil30:excl>
           ...
         </smil30:excl>
      </smil>  

      4) A SMIL 3.0 Tiny profile document that has been extended to use the 'foo' element from a fictitious SMIL 3.5 version of SMIL:

      <smil xmlns="http://www.w3.org/2007/07/SMIL30/Tiny"
            xmlns:smil35="http://www.example.org/2007/SMIL35/">
        <smil35:foo>
          ...
        </smil35:foo>
      </smil>
       

   2. No default namespace declaration is present on the smil root element in the document. The document will be processed as a SMIL 1.0 document.
   3. The namespace declaration is a valid name of an earlier release of a SMIL profile. For example, assume the namespace declaration is "http://www.w3.org/2001/SMIL20/Language". The document will be processed as a SMIL 2.0 document.
   4. Default namespace declaration on the smil root element unrecognized. A SMIL user agent will not recognize the document as any version of SMIL and must issue an error.
6. The user agent must support the following W3C Recommendations with regard to SMIL 3.0 content:
   • Complete support for the XML 1.1 specification (Extensible Markup Language (XML) 1.1) [XML11].
   • Complete support for inclusion of non-SMIL 3.0 namespaces within SMIL 3.0 content via Namespaces in XML [XML-NS]. A xmlns declaration or xmlns prefix declaration may be used on any element in the SMIL 3.0 document.
7. The user agent ignores namespace prefix qualified elements from unrecognized namespaces and must support the skip-content attributes. If no skip-content attributes are declared, the value of true is assumed.
8. The user agent ignores elements with unrecognized default namespace declarations and must support the skip-content attribute. If no skip-content attributes are declared, the value of true is assumed.
9. The user agent must issue an error for an attribute value which does not conform to the syntax specified for that attribute.
10. The detection of a syntax error in a SMIL 3.0 language Profile document must result in the user agent issuing an error and not playing the document.
11. When the hyphenated (deprecated) and the camelCase version of an attribute syntax are used in the same document, SMIL 3.0 user agents should take into account the camelCase version only.
12. Conforming SMIL 3.0 user agents must play SMIL 1.0 documents as specified in the SMIL 1.0 Recommendation [SMIL10] and SMIL 2.0 documents as specified in the SMIL 2.0 Recommendation [SMIL20].

The Web Accessibility Initiative is defining "User Agent Accessibility Guidelines 1.0" [UAAG]. Developers are encouraged to design user agents that satisfy at least the Level A requirements of that document. Should UAAG 1.0 become a W3C Recommendation, a future version of SMIL is likely to require Level A conformance to UAAG 1.0 as part of SMIL user agent conformance.

16.4.3 Extending a SMIL 3.0 Profile

In the future, a SMIL 3.0 profile may be extended by other W3C Recommendations, or by private extensions. For these extensions, the following rules must be obeyed:

• All elements introduced in extensions must have a skip-content attribute if it should be possible that their content is processed by SMIL 3.0 user agents.
• Private extensions must be introduced by defining a new XML namespace.

Conformant SMIL 3.0 user agents are prepared to handle documents containing extensions that obey these two rules.

16.4.4 Scalable Profiles

A scalable profile enables user agents of a wide range of complexity to render from a single, scalable, SMIL document intelligent presentations tailored to the capabilities of the target devices. A family of scalable SMIL profiles can be built using the SMIL 3.0 Tiny Profile plus additional sets of modules geared to the particular needs each profile addresses. A profile specifies scalability using the content control facilities to support application/device specific features via a namespace mechanism. This mechanism will enable the extension and sub-setting of SMIL 3.0 in a uniform way. The SMIL 3.0 namespace may be used with other XML namespaces as per [XML-NS], although such documents are not strictly conforming SMIL 3.0 documents as defined elsewhere. It is expected that future work by W3C may address ways to specify conformance for documents involving multiple namespaces.

Definition

A scalable SMIL 3.0 profile contains all the modules specified for SMIL host-level language conformance.

Additionally it may contain any one or more additional modules from the set defined by the SMIL 3.0 Modules.

XML namespace declaration using the xmlns attribute and XML internationalization xml:lang attributes are supported on all elements.

A scalable profile is specified by using the content control facilities via a namespace mechanism as follows:

1. The systemRequired attribute specifies a set of modules that are necessary to support the extended profile. The effective profile used by the document is defined as the union of the modules defined for SMIL 3.0 host-level language conformance and those specified in the systemRequired attribute.
2. The systemRequired attribute may always be specified on the root smil element. If the basis of the scalable profile also support the SMIL 3.0 ContentControl module, the systemRequired attribute may also be specified inline on elements other than the root element.

<smil xmlns="http://www.w3.org/ns/SMIL" version="3.0" baseProfile="Language">
  ...
</smil>

<smil xmlns="http://www.w3.org/2007/07/SMIL30/Mobile" 
      xmlns:BrushMedia="http://www.w3.org/2007/07/SMIL30/BrushMedia" >
  <head>
    <layout>
      <region xml:id="colorbox" top="0px" left="0px" height="50px" width="50px" />
    </layout>
  </head>
  <body>
    <switch>
      <seq systemRequired="BrushMedia">
        <brush dur="5s" color="#0000FF" region="colorbox"/>
        <brush dur="5s" color="#00FF00" region="colorbox"/>
        <brush dur="5s" color="#FF0000" region="colorbox"/>
      </seq>
      <seq>
        <img dur="5s" src="blue.jpg"  region="colorbox"/>
        <img dur="5s" src="green.jpg" region="colorbox"/>
        <img dur="5s" src="red.jpg"   region="colorbox"/>
      </seq>
    </switch>
  </body>
</smil>