3. Conformance Definition


This section is normative.

3.1. Document Conformance

This version of XHTML provides a definition of strictly conforming XHTML documents, which are restricted to tags and attributes from the XHTML 1.1 namespace.

3.1.1. Strictly Conforming Documents

A Strictly Conforming XHTML 1.1 Document is a document that requires only the facilities described as mandatory in this specification. Such a document must meet all of the following criteria:

  1. It must validate against the DTD found in Appendix B.

  2. The root element of the document must be <html>.

  3. The root element of the document must designate the XHTML 1.1 namespace using the xmlns attribute [XMLNAMES]. The namespace designator for XHTML 1.1 is http://www.w3.org/TR/xhtml11.

  4. There must be a DOCTYPE declaration in the document prior to the root element. If present, the public identifier included in the DOCTYPE declaration must reference the DTD found in Appendix B using its Formal Public Identifier. The system identifier may be modified appropriately.

     html PUBLIC "-//W3C//DTD XHTML 1.1//EN"

XHTML 1.1 Documents may be labeled with the Internet Media Type text/xml or application/xml.

Here is an example of a minimal XHTML 1.1 document.

<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.w3.org/TR/xhtml11/schema" xml:lang="en" lang="en">
    <title>Virtual Library</title>
    <p>Moved to <a href="http://vlib.org/">vlib.org</a>.</p>

Note that in this example, the XML declaration is included. An XML declaration like the one above is not required in all XML documents. XHTML document authors are strongly encouraged to use XML declarations in all their documents. Such a declaration is required when the character encoding of the document is other than the default UTF-8 or UTF-16.

3.2. User Agent Conformance

A conforming user agent must meet all of the following criteria:

  1. In order to be consistent with the XML 1.0 Recommendation [XML], the user agent must parse and evaluate an XHTML 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 [XML].
  2. When the user agent claims to support facilities defined within this specification or required by this specification through normative reference, it must do so in ways consistent with the facilities' definition.
  3. When a user agent processes a document of Internet media type text/xml, it shall only recognize attributes of type ID (e.g. the id attribute on most XHTML elements) as fragment identifiers.
  4. If a user agent encounters an element it does not recognize, it must render the element's content.
  5. If a user agent encounters an attribute it does not recognize, it must ignore the entire attribute specification (i.e., the attribute and its value).
  6. If a user agent encounters an attribute value it doesn't recognize, it must use the default attribute value.
  7. If it encounters an entity reference (other than one of the predefined entities) for which the User Agent has processed no declaration (which could happen if the declaration is in the external subset which the User Agent hasn't read), the entity reference should be rendered as the characters (starting with the ampersand and ending with the semi-colon) that make up the entity reference.
  8. When rendering content, User Agents that encounter characters or character entity references that are recognized but not renderable should display the document in such a way that it is obvious to the user that normal rendering has not taken place.
  9. XML does not specifically define whitespace handling characteristics for elements where the xml:space attribute is set to default. For all such elements, XHTML User Agents are required to suppress line breaks occurring immediately after the start tag or immediately prior to the end tag.