3. Conformance Definition

Contents

3.1. Document Conformance
- 3.1.1. Strictly Conforming Documents
3.2. User Agent Conformance

This section is normative.

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3.1. Document Conformance

3.1.1. Strictly Conforming Documents

DTD Bias

This section has a distinct DTD bias. We need to make it clear that either the DTD or the Schema can be used to validate XHTML 2.0 documents.

A strictly conforming XHTML 2.0 document is a document that requires only the facilities described as mandatory in this specification. Such a document must meet all the following criteria:

The document must conform to the constraints expressed in Appendix B - XHTML 2.0 Schema or Appendix D - XHTML 2.0 Document Type Definition.
The root element of the document must be html.
The root element of the document must contain an xmlns declaration for the XHTML 2.0 namespace [XMLNAMES]. The namespace for XHTML is defined to be http://www.w3.org/2002/06/xhtml2. An example root element might look like:
```
<html xmlns="http://www.w3.org/2002/06/xhtml2" xml:lang="en">
```
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 E using its Formal Public Identifier. The system identifier may be modified appropriately.
```
<!DOCTYPE
 html PUBLIC "-//W3C//DTD XHTML 2.0//EN"
 "TBD">
```

Here is an example of an XHTML 2.0 document.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 2.0//EN"
    "TBD">
<html xmlns="http://www.w3.org/2002/06/xhtml2" xml:lang="en">
  <head>
    <title>Virtual Library</title>
  </head>
  <body>
    <p>Moved to <a href="http://vlib.org/">vlib.org</a>.</p>
  </body>
</html>

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 and no encoding was determined by a higher-level protocol.

3.2. User Agent Conformance

A conforming user agent must meet all user agent conformance requirements defined in [XHTMLMOD].