XML's many applications include one traditionally handled by HTML, document source. Sometimes you want to include some HTML in your XML source; particularly when styling your XML with XSL to HTML, you may want some literal HTML in the output. In some cases, you'd just like to include some well-formed mixed-content HTML in your XML, and not worry too much about controlling its structure.

Advertisement

On this topic Recruiters endorse HR-XML proposal IBM will not charge royalties for ebXML patent XML presses the publishing business Speech technology for applications inches forward Corel jumps on XML, .Net for enterprise push

Writing explicit XSL rules for each HTML tag would be tedious and hard to maintain. This week, I'll present a quick shortcut that allows you to include arbitrary mixed-content HTML in your XSL stylesheet's output.

The XSL stylesheet's input includes some XML document, constrained by (that is, validated against) a particular DTD. To define the element containing the arbitrary HTML's content model, simply define content models for each of the HTML elements you want to use and their attribute lists. For example, define the <.a> tag for hyperlinks like this:

<.!ELEMENT a (#PCDATA)*>

<.!ATTLIST a
href CDATA #IMPLIED target CDATA #IMPLIED name CDATA #IMPLIED>

(This example is simplified, since it allows only unformatted text inside the hyperlink text node.) Create a definition like this for each HTML tag you wish to use. After you've defined the tags, define a parameter entity that includes all of the HTML "pass-through" tags you've defined:

<.!ENTITY % htmlpassthru
"a|i|b|code|br|tr|td|th|img|font|em">

Anywhere in the DTD you want to include mixed-content HTML, use this parameter entity in the DTD. For example:

<.!ELEMENT HtmlHelpText (#PCDATA|%htmlpassthru;)*>

Now for the stylesheet. Defining a separate rule for each possible HTML element within a HtmlHelpText element would be extremely tedious. Fortunately, a single rule can handle all such elements. Define an XSL rule that matches the tag name AND uses <.xsl:copy-of> to copy the entire node (including attributes) to the output.

<.!-- EXAMPLE XSL stylesheet -->

<.xsl:template
match="a|i|b|code|br|tr|td|th|img|font|em"> <.xsl:copy-of select="."/> <./xsl:template>

<.!-- End EXAMPLE -->

Any nodes in the XML input tree with these tags will be copied to the output structure unmodified, attributes and all.

This technique is somewhat "quick-and-dirty". Choosing XHTML, which reformulates HTML as XML and brings XML's extensibility and structure control into the world of HTML, would be a better solution. But that's a topic for another newsletter.