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30 April 2002

# Appendix G: Conformance Criteria

### Contents

This appendix is normative.

## G.1 Introduction

In order to ensure that SVG-family documents are maximally portable among SVG-family user agents, this specification rigidly defines conformance requirements for both of these and for SVG-family document types. While the conformance definitions can be found in this appendix, they necessarily reference normative text within this document and within other related specifications. It is only possible to fully comprehend the conformance requirements of SVG through a complete reading of all normative references.

## G.2 Conforming SVG Document Fragments

An SVG document fragment is a Conforming SVG Document Fragment if it adheres to the specification described in this document (Scalable Vector Graphics (SVG) Specification) including SVG's DTD (see Document Type Definition) and also:

- (relative to XML) is well-formed.
- if all non-SVG namespace elements and attributes and all xmlns attributes which refer to non-SVG namespace elements are removed from the given document, and if an appropriate XML declaration (i.e., `<?xml...?>`) is included at the top of the document, and if an appropriate document type declaration (i.e., `<!DOCTYPE svg ... >`) which points to the SVG DTD is included immediately thereafter, the result is a valid XML document.
- conforms to the following W3C Recommendations:
  - the XML 1.0 specification (Extensible Markup Language (XML) 1.0).
  - (if any namespaces other than SVG are used in the document) Namespaces in XML.
  - any use of CSS shall conform to Cascading Style Sheets, level 2 CSS2 Specification.
  - any references to external style sheets shall conform to Associating stylesheets with XML documents.

The SVG language or these conformance criteria provide no designated size limits on any aspect of SVG content. There are no maximum values on the number of elements, the amount of character data, or the number of characters in attribute values.

## G.3 Conforming SVG Stand-Alone Files

A file is a Conforming SVG Stand-Alone File if:

- it is an XML document.
- its root element is an 'svg' element.
- it conforms to the criteria for Conforming SVG Document Fragment.

## G.4 Conforming SVG Included Document Fragments

SVG document fragments can be included within parent XML documents using the XML namespace facilities described in Namespaces in XML.

An SVG document fragment that is included within a parent XML document is a Conforming Included SVG Document Fragment if the SVG document fragment, when taken out of the parent XML document, conforms to the SVG Document Type Definitions (DTD).

In particular, note that individual elements from the SVG namespace cannot be used by themselves. Thus, the SVG part of the following document is not conforming:

    <?xml version="1.0" standalone="no"?>
    <!DOCTYPE SomeParentXMLGrammar PUBLIC "-//SomeParent"
      "http://SomeParentXMLGrammar.dtd">
    <ParentXML>
      <!-- Elements from ParentXML go here -->

      <!-- The following is not conforming -->
      <z:rect xmlns:z="http://www.w3.org/2000/svg"
                x="0" y="0" width="10" height="10" />

      <!-- More elements from ParentXML go here -->
    </ParentXML>

Instead, for the SVG part to become a Conforming Included SVG Document Fragment, the file could be modified as follows (the example below shows the use of Stylable SVG):

    <?xml version="1.0" standalone="no"?>
    <!DOCTYPE SomeParentXMLGrammar PUBLIC "-//SomeParent"
      "http://SomeParentXMLGrammar.dtd">
    <ParentXML>
      <!-- Elements from ParentXML go here -->

      <!-- The following is conforming -->
      <z:svg xmlns:z="http://www.w3.org/2000/svg"
             width="100px" height="100px" >
        <z:rect x="0" y="0" width="10" height="10" />
      </z:svg>

      <!-- More elements from ParentXML go here -->
    </ParentXML>

## G.5 Conforming SVG Host Language Documents

It is possible to modify existing document types and define wholly new document types using both modules defined in this specification and other modules. Such a document type is "SVG Host Language Conforming" when it meets the following criteria:

1. The document type must be defined using one of the implementation methods defined by the W3C. Currently this is limited to XML DTDs, but XML Schema will be available soon. The rest of this section refers to "DTDs" although other implementations are possible.
2. The DTD which defines the document type must have a unique identifier as defined in Naming Rules that uses the string "SVG" in its first token of the public text description.
3. For each of the W3C-defined modules that are included, all of the elements, attributes, types of attributes (including any required enumerated value lists), and any required minimal content models must be included (and optionally extended) in the document type's content model. When content models are extended, all of the elements and attributes (along with their types or any required enumerated value lists) required in the original content model must continue to be required.
4. The DTD which defines the document type may define additional elements and attributes. However, these must be in their own XML namespace.

## G.6 Conforming SVG Integration Set Documents

It is also possible to define document types that are based upon SVG, but do not adhere to its structure. Such a document type is "SVG Integration Set Conforming" when it meets the following criteria:

1. The document type must be defined using one of the implementation methods defined by the W3C. Currently this is limited to XML DTDs, but XML Schema will be available soon. The rest of this section refers to "DTDs" although other implementations are possible.
2. The DTD which defines the document type must have a unique identifier as defined in Naming Rules that uses the string "SVG" NOT in its first token of the public text description.
3. For each of the W3C-defined modules that are included, all of the elements, attributes, types of attributes (including any required enumerated lists), and any required minimal content models must be included (and optionally extended) in the document type's content model. When content models are extended, all of the elements and attributes (along with their types or any required enumerated value lists) required in the original content model must continue to be required.
4. The DTD which defines the document type may define additional elements and attributes. However, these must be in their own XML namespace.

## G.7. SVG Family Module Conformance

This specification defines a method for defining SVG-conforming modules. A module conforms to this specification when it meets all of the following criteria:

1. The document type must be defined using one of the implementation methods defined by the W3C. Currently this is limited to XML DTDs, but XML Schema will be available soon. The rest of this section refers to "DTDs" although other implementations are possible.
2. The DTD which defines the module must have a unique identifier as defined in Naming Rules.
3. When the module is defined using an XML DTD, the module must insulate its parameter entity names through the use of unique prefixes or other, similar methods.
4. The module definition must have a prose definition that describes the syntactic and semantic requirements of the elements, attributes, and/or content models that it declares.
5. The module definition must not reuse any element names that are defined in other W3C-defined modules, except when the content model and semantics of those elements are either identical to the original or an extension of the original, or when the reused element names are within their own namespace (see below).
6. The module definition's elements and attributes must be part of an XML namespace. If the module is defined by an organization other than the W3C, this namespace must NOT be the same as the namespace in which other W3C modules are defined.

## G.8. SVG Family Document Conformance

A conforming SVG family document is a valid instance of a conforming SVG Host Language Document.

## G.9 Conforming SVG Generators

A Conforming SVG Generator is a program which:

- always creates at least one of Conforming SVG Document Fragments, Conforming SVG Stand-Alone Files or Conforming SVG Included Documents.
- does not create non-conforming SVG document fragments of any of the above types.

Additionally, an authoring tool which is a Conforming SVG Generator conforms to all of the Priority 1 accessibility guidelines from the document "Authoring Tool Accessibility Guidelines 1.0" [ATAG] that are relevant to generators of SVG content. (Priorities 2 and 3 are encouraged but not required for conformance.)

SVG generators are encouraged to follow W3C developments in the area of internationalization. Of particular interest is the W3C Character Model and the concept of Webwide Early Uniform Normalization, which promises to enhance the interchangability of Unicode character data across users and applications. Future versions of the SVG specification are likely to require support of the W3C Character Model in Conforming SVG Generators.

## G.10 Conforming SVG Interpreters

An SVG interpreter is a program which can parse and process SVG document fragments. Examples of SVG interpreters are server-side transcoding tools (e.g., a tool which converts SVG content into modified SVG content) or analysis tools (e.g., a tool which extracts the text content from SVG content). An SVG viewer also satisfies the requirements of an SVG interpreter in that it can parse and process SVG document fragments, where processing consists of rendering the SVG content to the target medium.

In a Conforming SVG Interpreter, the XML parser must be able to parse and process all XML constructs defined within [XML10] and [XML-NS].

There are two sub-categories of Conforming SVG Interpreters:

- Conforming Static SVG Interpreters must be able to parse and process the static language features of SVG that correspond to the feature string "org.w3c.svg.static" (see Feature strings).
- In addition to the requirements for the static category, Conforming Dynamic SVG Interpreters must be able to parse and process the language features of SVG that correspond to the feature string "org.w3c.svg.dynamic" (see Feature strings) and which support all of the required features in the SVG DOM described in this specification.

A Conforming SVG Interpreter must parse any SVG document correctly. It is not required to interpret the semantics of all features correctly.

Note: A transcoder from SVG into another graphics representation, such as an SVG-to-raster transcoder, represents a viewer, and thus viewer conformance criteria apply. (See Conforming SVG Viewers.)

## G.11 Conforming SVG Viewers

An SVG viewer is a program which can parse and process an SVG document fragment and render the contents of the document onto some sort of output medium such as a display or printer; thus, an SVG Viewer is also an SVG Interpreter.

There are two sub-categories of Conforming SVG Viewers:

- Conforming Static SVG Viewers support the static language features of SVG that correspond to the feature string "org.w3c.svg.static" (see Feature strings). This category often corresponds to platforms and environments which only render static documents, such as printers.
- Conforming Dynamic SVG Viewers support the language features of SVG that correspond to the feature string "org.w3c.svg.dynamic" (see Feature strings). This category often applies to platforms and environments such as common Web browsers which support user interaction and dynamic document content (i.e., documents whose content can change over time). (User interaction includes support for hyperlinking, events [e.g., mouse clicks], text selection, zooming and panning [see Interactivity]. Dynamic document content can be achieved via declarative animation or by scripts modifying the SVG DOM.)

Specific criteria that apply to both Conforming Static SVG Viewers and Conforming Dynamic SVG Viewers:

- The program must also be a Conforming SVG Interpreter,
- For interactive user environments, facilities must exist for zooming and panning of stand-alone SVG documents or SVG document fragments embedded within parent XML documents.
- In environments that have appropriate user interaction facilities, the viewer must support the ability to activate hyperlinks.
- If printing devices are supported, SVG content must be printable at printer resolutions with the same graphics features available as required for display (e.g., the specified colors must be rendered on color printers).
- On systems where this information is available, the parent environment must provide the viewer with information about physical device resolution. In situations where this information is impossible to determine, the parent environment shall pass a reasonable value for device resolution which tends to approximate most common target devices.
- The viewer must support JPEG [JPEG] and PNG [PNG10] image formats.
- Resampling of image data must be consistent with the specification of property 'image-rendering'.
- The viewer must support alpha channel blending of the image of the SVG content onto the target canvas.
- SVG implementations which support the HTTP protocol must correctly support gzip-encoded SVG data streams according to the HTTP 1.1 specification [RFC2616]; thus, the client must specify "Accept-Encoding: gzip" [ HTTP-ACCEPT-ENCODING] on its request-header field and then decompress any gzip-encoded data streams that are downloaded from the server. If the implementation supports progressive rendering, the implementation should also support progressive rendering of compressed data streams.
- The viewer must support base64 encoded content using the "data:" protocol [RFC2397] wherever URI referencing of whole documents (such as raster images, SVG documents, fonts and color profiles) is permitted within SVG content. (Note: fragments of SVG content which do not constitute an entire SVG document are not available using the "data:" protocol.)
- The viewer must support the following W3C Recommendations with regard to SVG content:
  - complete support for the XML 1.0 specification [XML10].
  - complete support for inclusion of non-SVG namespaces within SVG content as defined in "Namespaces in XML" [XML-NS]. (Note that data from non-SVG namespaces are included in the DOM but are otherwise ignored.)
- All visual rendering must be accurate to within one device pixel to the mathematically correct result.
- On systems which support accurate sRGB [SRGB] color, all sRGB color computations and all resulting color values must be accurate to within one sRGB color component value, where sRGB color component values range from 0 to 255.

Although anti-aliasing support is not a strict requirement for a Conforming SVG Viewer, it is highly recommended for display devices. Lack of anti-aliasing support will generally result in poor results on display devices.

Specific criteria that apply to only Conforming Dynamic SVG Viewers:

- In Web browser environments, the viewer must have the ability to search and select text strings within SVG content.
- If display devices are supported, the viewer must have the ability to select and copy text from SVG content to the system clipboard.
- The viewer must have complete support for an ECMAScript binding of the SVG Document Object Model.

The Web Accessibility Initiative [WAI] is defining "User Agent Accessibility Guidelines 1.0" [UAAG]. Viewers are encouraged to conform to the Priority 1 accessibility guidelines defined in this document, and preferably also Priorities 2 and 3. Once the guidelines are completed, a future version of this specification is likely to require conformance to the Priority 1 guidelines in Conforming SVG Viewers.

A higher order concept is that of a Conforming High-Quality SVG Viewer, with sub-categories Conforming High-Quality Static SVG Viewer and Conforming High-Quality Dynamic SVG Viewer.

Both a Conforming High-Quality Static SVG Viewer and a Conforming High-Quality Dynamic SVG Viewer must support the following additional features:

- Professional-quality results with good processing and rendering performance and smooth, flicker-free animations.
- On low-resolution devices such as display devices at 150dpi or less, support for smooth edges on lines, curves and text. (Smoothing is often accomplished using anti-aliasing techniques.)
- Color management via ICC profile support (i.e., the ability to support colors defined using ICC profiles).
- Resampling of image data must conform to the requirements for Conforming High-Quality SVG Viewers as specified in the description of property 'image-rendering'.
- At least double-precision floating point computation on coordinate system transformation numerical calculations.

A Conforming High-Quality Dynamic SVG Viewer must support the following additional features:

- Progressive rendering and animation effects (i.e., the start of the document will start appearing and animations will start running in parallel with downloading the rest of the document).
- Restricted screen updates (i.e., only required areas of the display are updated in response to redraw events).
- Background downloading of images and fonts retrieved from a Web server, with updating of the display once the downloads are complete.

A Conforming SVG Viewer must be able to apply styling properties to SVG content using presentation attributes.

If the user agent includes a CSS2 capability, a Conforming SVG Viewer must support CSS styling of SVG content and must support all features from CSS2 (Cascading Style Sheets, level 2 CSS2 Specification) that are described in this specification as applying to SVG (see properties shared with CSS and XSL, Styling with CSS and Facilities from CSS and XSL used by SVG). The supported features from CSS2 must be implemented in accordance with the conformance definitions from the CSS2 specification.

If the user agent includes an HTML or XHTML viewing capability or can apply CSS/XSL styling properties to XML documents, then a Conforming SVG Viewer must support resources of MIME type "image/svg+xml" wherever raster image external resources can be used, such as in the HTML or XHTML 'img' element and in CSS/XSL properties that can refer to raster image resources (e.g., 'background-image').

## G.12 Naming Rules

SVG Host Language document types must adhere to strict naming conventions so that it is possible for software and users to readily determine the relationship of document types to SVG. The names for document types implemented as XML document type definitions are defined through Formal Public Identifiers (FPIs). Within FPIs, fields are separated by double slash character sequences (`//`). The various fields must be composed as follows:

1. The leading field must be "-" to indicate a privately defined resource.
2. The second field must contain the name of the organization responsible for maintaining the named item. There is no formal registry for these organization names. Each organization should define a name that is unique. The name used by the W3C is, for example, `W3C`.
3. The third field contains two constructs: the public text class followed by the public text description. The first token in the third field is the public text class which should adhere to ISO 8879 Clause 10.2.2.1 Public Text Class. Only SVG Host Language conforming documents should begin the public text description with the token "SVG". The public text description should contain the string "SVG" if the document type is Integration Set conforming. The field must also contain an organization-defined unique identifier (e.g., MyML 1.0). This identifier should be composed of a unique name and a version identifier that can be updated as the document type evolves.
4. The fourth field defines the language in which the item is developed (e.g., `EN`).

Using these rules, the name for an SVG Host Language conforming document type might be `-//MyCompany//DTD XHTML MyML 1.0//EN`. The name for an SVG family conforming module might be `-//MyCompany//ELEMENTS XHTML MyElements 1.0//EN`. The name for an SVG Integration Set conforming document type might be `-//MyCompany//DTD Special Markup with SVG//EN`.

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