XSLT and XQuery Serialization 4.0

6 XHTML Output Method

The XHTML output method serializes the input tree as XML, using the HTML compatibility guidelines defined in the XHTML specification ([XHTML 1.0] or the XHTML syntax of HTML5 (see [HTML5]).

The default value of the html-version serialization parameter for this method is 5.0, and all references to the value of this parameter assume this default when the parameter is absent. The value of the parameter is a decimal, so the values 5 and 5.0 are equivalent.

[Definition: The term with HTML5 is used in this specification to qualify rules that apply only when the effective version of the html-version serialization parameter is 5.0.]

[Definition: The term prior to HTML5 is used in this specification to qualify rules that apply only when the effective version of the html-version serialization parameter is less than 5.0.]

[Definition: An element node is recognized as an HTML element by the XHTML output method if either of the following conditions is true:

• the element node is in the XHTML namespace; or

• With HTML5: the element has a null namespace URI and the local part of the name is equal to the name of an element defined by HTML5 [HTML5], making the comparison without regard to case.

]

It is entirely the responsibility of the supplier of the input tree to ensure that it conforms to the relevant specification, this being:

• With HTML5, the XHTML syntax of HTML5;

• Prior to HTML5, the [XHTML 1.0] or [XHTML 1.1] specification.

It is not an error if the input tree is invalid XHTML. Equally, it is entirely under the control of the supplier of the input tree whether the output conforms to XHTML 1.0 Strict, XHTML 1.0 Transitional, the XHTML syntax of HTML5 (see [HTML5]), [POLYGLOT] or any other specific definition of XHTML.

The serialization of the input tree follows the same rules as for the XML output method, with the general exceptions noted below and parameter-specific exceptions in 6.1 The Influence of Serialization Parameters upon the XHTML Output Method. These differences are based on the HTML compatibility guidelines published in Appendix C of [XHTML 1.0] and on [POLYGLOT], both of which are designed to ensure that as far as possible, XHTML is rendered correctly on user agents designed originally to handle HTML.

With HTML5 the input tree is first subjected to prefix normalization.

[Definition: During prefix normalization, any element node in the input tree that is in one of the XHTML namespace, the SVG namespace or the MathML namespace has its name replaced by the local part of its name. Such an element node is given a default namespace node whose value is the element’s namespace URI. Any namespace node for any of those three namespaces that was previously present on any element node in the input tree is also removed, unless the prefix that that namespace node declared is used as the prefix on the name of an attribute on that element or an ancestor of that element.]

The process of prefix normalization is equivalent to replacing the input tree with the result of the transformation described by this XSLT stylesheet, with the root of the input tree as the initial context value.

<xsl:stylesheet
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
    version="4.0"
    xmlns:xhtml="http://www.w3.org/1999/xhtml"
    xmlns:svg="http://www.w3.org/2000/svg"
    xmlns:mathml="http://www.w3.org/1998/Math/MathML">
  <xsl:template match="xhtml:*|svg:*|mathml:*">
    <xsl:element name="{local-name()}" 
                 namespace="{namespace-uri()}">
      <xsl:apply-templates select="@*|namespace::*|node()"/>
    </xsl:element>
  </xsl:template>

  <xsl:template match="node()|@*|namespace::*">
    <xsl:copy copy-namespaces="no">
      <xsl:apply-templates select="@*|namespace::*|node()"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template
    match="namespace::*[. eq 'http://www.w3.org/1999/xhtml']|
           namespace::*[. eq 'http://www.w3.org/2000/svg']|
           namespace::*[. eq 'http://www.w3.org/1998/Math/MathML']"/>
</xsl:stylesheet>

• [Definition: The following XHTML elements have an EMPTY content model: area, base, br, col, embed, hr, img, input, link, meta, basefont, frame, isindex, and param.] [Definition: The void elements of HTML5 are area, base, br, col, embed, hr, img, input, keygen, link, meta, param, source, track and wbr.]

  [Definition: An element node is expected to be empty if it is recognized as an HTML element and:

  • With HTML5, the element is a void element.

  • Prior to HTML5, the content model is EMPTY.

  ]

  If an element node that has no child nodes is not expected to be empty, and:

  • With HTML5, the HTML element is not a void element, or

  • Prior to HTML5, the content model of the HTML element is not EMPTY (for example, an empty title or paragraph)

  then the serializermust not use the minimized form. That is, it must output <p></p> and not <p />.

• If an element that has no children is expected to be empty, the serializermust use the minimized tag syntax, for example <br />, as the alternative syntax <br></br> allowed by XML gives uncertain results in many legacy user agents. If the html-version serialization parameter has a value less than 5.0, the serializermust include a space before the trailing />, e.g. <br />, <hr /> and <img src="karen.jpg" alt="Karen" />.

• Prior to HTML5, the serializermust not use the entity reference ' which, although defined in XML and therefore in XHTML, is not defined in versions of HTML prior to HTML5, and is not recognized by all HTML user agents.

• With HTML5, the serializershould output namespace declarations in a way that is consistent with the requirements of [POLYGLOT].

  Prior to HTML5, the serializershould output namespace declarations in a way that is consistent with the requirements of the XHTML DTD if this is possible.

  The XHTML 1.0 DTDs require the declaration xmlns="http://www.w3.org/1999/xhtml" to appear on the html element, and only on the html element. The [POLYGLOT] specification permits namespace declarations to appear in a conforming document, but restricts the elements on which they can appear. The serializermust output namespace declarations that are consistent with the namespace nodes present in the result tree, but it must avoid outputting redundant namespace declarations on elements where the DTD would make them invalid, for versions prior to HTML5, or where they are not permitted by [POLYGLOT], for serialization according to the syntax of HTML5.

  Note:

  If the html element is generated by an XSLT literal result element of the form <html xmlns="http://www.w3.org/1999/xhtml"> ... </html>, or by an XQuery direct element constructor of the same form, then the html element in the result document will have a node name whose prefix is "", which will satisfy the requirements of the DTD. In other cases the prefix assigned to the element is implementation-dependent.

7 HTML Output Method

The HTML output method serializes the input tree as HTML.

<xsl:stylesheet version="2.0" 
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html" version="4.0"/>
<xsl:template match="/">
  <html>
    <xsl:apply-templates/>
  </html>
</xsl:template>
...
</xsl:stylesheet>

In the example, the version attribute of the xsl:output element indicates the version of the HTML Recommendation [HTML] to which the serialized result is to conform.

[Definition: The requested HTML version is the value of the html-version serialization parameter if present; otherwise the value of the version serialization parameter if present; otherwise 5.0.]

This document provides the normative definition of serialization for the HTML output method if the requested HTML version has the lexical form of a value of type decimal whose value is 1.0 or greater, but no greater than 5.0. For any other requested HTML version, the behavior is implementation-defined. In that case the implementation-defined behavior may supersede all other requirements of this recommendation.

An implementation is required to behave as specified in this document when the requested version is 5.0. If the requested version is greater than or equal to 1 but less than 5.0, then the processor may behave as if the requested version were 5.0.

It is entirely the responsibility of the supplier of the input tree to ensure that it conforms to the relevant HTML specification. It is not an error if the input tree is invalid HTML. Equally, it is entirely under the control of the supplier of the input tree whether the output conforms to HTML. If the result tree is valid HTML, the serializermust serialize the result in a way that conforms with the requested HTML version.