xsl:stylesheet and xsl:transform (XML in a Nutshell, 2nd Edition)

8.2. xsl:stylesheet and xsl:transform

An XSLT stylesheet is an XML document. It can and generally should have an XML declaration. It can have a document type declaration, though most stylesheets do not. The root element of this document is either stylesheet or transform. These are synonyms for each other. You can use either stylesheet or transform as you prefer. There is absolutely no difference between them, aside from the name. They both have the same possible children and attributes. They both mean the same thing to an XSLT processor.

The stylesheet and transform elements, like all other XSLT elements, are in the http://www.w3.org/1999/XSL/Transform namespace. This namespace is customarily mapped to the xsl prefix so that you write xsl:transform or xsl:stylesheet rather than simply transform or stylesheet.

As well as the xmlns:xsl attribute declaring this prefix mapping, the root element must have a version attribute with the value 1.0. Thus, a minimal XSLT stylesheet, with only the root element and nothing else, is as shown in Example 8-2.

WARNING: This namespace URI must be exactly correct. If even so much as a single character is wrong, the stylesheet processor will output the stylesheet itself instead of either the input document or the transformed input document. There's a reason for this (see Section 2.3 of the XSLT 1.0 specification, Literal Result Element as Stylesheet, if you really want to know), but the bottom line is that this weird behavior looks very much like a bug in the XSLT processor if you're not expecting it. If you ever do see your stylesheet processor spitting your stylesheet back out at you, the problem is almost certainly an incorrect namespace URI.

TIP: Internet Explorer 5.0 and 5.5 partially support a very old and out-of-date working draft of XSLT, as well as various Microsoft extensions to this old working draft. They do not support XSLT 1.0, and indeed no XSLT stylesheets in this book work in IE5. Stylesheets that are meant for Microsoft XSLT can be identified by their use of the http://www.w3.org/TR/WD-xsl namespace. IE6 supports both http://www.w3.org/1999/XSL/Transform and http://www.w3.org/TR/WD-xsl. Good XSLT developers don't use http://www.w3.org/TR/WD-xsl and don't associate with developers who do.

Example 8-2. A minimal XSLT stylesheet

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

</xsl:stylesheet>

Perhaps a little surprisingly, this is a complete XSLT stylesheet; an XSLT processor can apply it to an XML document to produce an output document. Example 8-3 shows the effect of applying this stylesheet to Example 8-1.

Example 8-3. people.xml transformed by the minimal XSLT stylesheet

<?xml version="1.0" encoding="utf-8"?>

      Alan
      Turing

    computer scientist
    mathematician
    cryptographer

      Richard
      P
      Feynman

    physicist
    Playing the bongoes

You can see that the output consists of a text declaration plus the text of the input document. In this case, the output is a well-formed external parsed entity, but it is not itself a complete XML document.

Markup from the input document has been stripped. The net effect of applying an empty stylesheet, like Example 8-2, to any input XML document is to reproduce the content but not the markup of the input document. To change that, we'll need to add template rules to the stylesheet telling the XSLT processor how to handle the specific elements in the input document. In the absence of explicit template rules, an XSLT processor falls back on built-in rules that have the effect shown here.