Get acquainted with the basic elements of an XSLT stylesheet.
You had a close brush with XSLT in the hack that discussed converting text to XML [Hack #18] , but you didn’t see much more than the stylesheet’s name. Here is the complete stylesheet, time.xsl :
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="Import"> <xsl:apply-templates select="Row"/> </xsl:template> <xsl:template match="Row"> <time timezone="{@timezone}"> <xsl:copy-of select="hour|minute|second"/> <xsl:apply-templates select="atomic"/> </time> </xsl:template> <xsl:template match="atomic"> <xsl:copy> <xsl:attribute name="signal">true</xsl:attribute> </xsl:copy> </xsl:template> </xsl:stylesheet>
An XSLT stylesheet has two possible
document elements,
stylesheet
and transform
(see
line 1). Both have identical attributes; in fact, the only difference
between the two is that they have different names, but
stylesheet
seems more popular with developers than
transform
.
The version
attribute is required. Some XSLT
processors support a value of 1.1 or 2.0, in support of those
versions of the XSLT specs, but 1.0 is the most commonly used value.
(Version 1.1 of XSLT is not and will never be a W3C recommendation,
so any support for it is processor-dependent.) The namespace
declaration is also required if you want an XSLT processor to
recognize the XSLT markup. The namespace name for XSLT 1.0 is
http://www.w3.org/1999/XSL/Transform
. The prefix
xsl
is conventional: you can’t
get very far with XSLT without using a namespace prefix. Believe me,
I’ve tried.
Templates are at the heart of what XSLT does. Templates match nodes in the document being processed, and when a node is matched, the content of the template is instantiated or executed. Nodes are the building blocks of an XML document. According to the XPath 1.0 data model (http://www.w3.org/TR/xpath#data-model), seven nodes are identifiable within an XML document: root, element, attribute, text, comment, processing instruction, and namespace nodes.
XSLT has some built-in templates that are instantiated in the absence of matched templates. In other words, if nodes are matched but no templates are found for a processed document, built-in templates will automatically be instantiated, returning text nodes, among other things.
This stylesheet has three templates (lines 3, 7, and 14). The first
template matches the element Import
, the document
element of a converted text document in xmlspy (see
[Hack #18]
). When an
apply-templates
element is encountered, it processes
all the children of the matched node. If
apply-templates
has a select
attribute, it processes only the selected nodes. The
apply-templates
element on line 4 attempts to find
other templates in the stylesheet that match the
Row
element, the child of
Import
.
The template beginning on line 7 matches the Row
element. When found, the template is instantiated: a
literal result element
time
is output to the result tree, with a
timezone
attribute taking its value from an
attribute in the source tree. A literal result element is output
literally (appearing directly in the result), and is subject to a
well-formedness check by the processor, as is the entire stylesheet.
The braces on line 8 hold something called an attribute
value template. This is sort of a template within a
template. When the XSLT processor encounters a
timezone
attribute in the source tree, it grabs
the value held by the attribute and places it in the value of the
attribute represented in the stylesheet.
Line 9 contains a
copy-of
element that makes copies of the
hour
, minute
, and
second
nodes in the result tree.
apply-templates
(line 10) searches for a template
matching atomic
elements.
copy-of
makes deep copies of elements, copying
attributes if present.
When the template on line 14 matches an atomic
element, it makes a copy of the element with the
copy
element, adding a signal
attribute (line 16) to it in the output using an
attribute
instruction element (there are
instruction elements for elements, attributes, comments, and more).
copy
makes a shallow copy of a node, leaving
attribute nodes behind.
18.117.182.179