Transformation Without Change - Page 8
October 28, 2002
The stylesheet has added some code to the beginning of the translated <body>
element, but hasn't yet done anything with the original contents of the <body>
element. That's the job of the next line, <xsl:apply-templates />. This line says "Work through
all of the contents of the <body>
element, and perform any other transformations you need to on any tags you
find". In our next example, we'll create some more template transformations
for some other elements, but for now we don't want to change anything else
at all. We want the rest of the <body> element contents to be passed
through unchanged.
Even though we want the content to remain unchanged, we still need to specify
a transformation for the other tags in our page – <html>, <head>,
<title>, <style>, <b>, <h1>, <h2>, <ul> and <li>. If we don't specify a transformation
for these tags, they will be ignored, leaving us with a mass of unformatted
text and no tags at all. This isn't nice. We use the Identity Transformation
to pass these tags through unchanged.
The Identity Transformation is specified in those curious few lines right
in the middle of headerfooter_1.xsl:
<xsl:template
match="node()|@*">
<xsl:copy>
<xsl:apply-templates
select="node()|@*"/>
</xsl:copy>
</xsl:template>
The Identity Transformation is a transformation that leaves everything just
the way it found it. It matches every part of our source XML document for
which we haven't given a specific rule, and passes it through unchanged –
let's look at how this works now.
How Does the Identity Transformation Work?
Very often when writing a stylesheet, we find that we only
want to make small changes to the input document. If this is the case,
then it's easiest to pass through almost everything unchanged, and just match
the few elements that need alteration.
We do this using the Identity Transformation introduced above:
<xsl:template match="node()|@*">
<xsl:copy>
<xsl:apply-templates
select="node()|@*" />
</xsl:copy>
</xsl:template>
This template matches both node() (any node in the input document) and @* (any attribute), so it matches everything.
When it matches, it uses <xsl:copy> to create an identical copy of the item it
has matched, and then uses <xsl:apply-templates>
to process the contents of the item if there are any.
If this was the only template in a stylesheet, it would produce an output
document functionally the same as the input one. The identity transformation
isn't appropriate when the output document needs to be considerably different
from the input document.
Normally, as we have done in Example 1
above, we would use the identity template alongside others that add, remove,
or alter a few nodes. These other templates, such as the template matching
<body> that we defined above,
will be used rather than the identity template for the nodes that they match.
Each element or attribute in the source XML document can only be matched by
one template (as we'll see later in this chapter, the most specific template
available is used in XSLT 1.0); this is why we had to specifically copy the
<body> element to our output document
rather than relying on the identity template to do it for us.
Adding the Footer
Lastly, we want to add some footer text after the unchanged <body> element contents. This is performed
by the end section of our <body>
element template:
<hr/>
Copyright 2002 DinosaurOrg.
</body>
</xsl:template>
After the body content has been passed through unchanged, these lines add
some footer HTML to the page and then close the <body> tag. We then close our body <xsl:template>
element, to tell the XSLT processor we have finished dealing with the <body> element.
Finally, the last line of headerfooter_1.xsl
tidies up the stylesheet with the line </xsl:stylesheet>.
We're done!
You Too Can Transform Your <body> - Page 7
Practical XML for the Web
Specifying Stylesheets for Different Browsers - Page 9
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