Re: [xsl] RE: unbelievable often asked question

[Mike Brown <mike@xxxxxxxx>]

Hubert Holtz wrote:
> I often visit tutorial-sites to get my informations (and now this great
> mail-list) and there was no "and", only a | for or.

"|" never really means "or".

In an XSLT pattern, which is what goes in a "match" attribute, it's just a
separator between node tests when used in a pattern. Depending on how you like 
to interpret your code into English, you might use the words "or" or "and" 
informally.

For example, <xsl:template match="foo|bar"> says this template is a good match
for a node that matches the test foo (element named foo in no namespace), and
it is also a good match for a node that matches the test bar (element named
bar in no namespace). Since a programmer might be used to reading "|" as
"or", it would be just as correct to say "this template is a good match for a
foo or a bar".

In an XPath expression, "|" is a set union operator.

In mathematics, a set is an unordered group of values, typically written (in
math, not XPath) as a comma-separated list inside curly braces: {1,2,3,4}.
Order doesn't matter. The union of two sets is the result of merging them and
eliminating duplicates. The union of {1,2,3,4} and {2,3,5} is {1,2,3,4,5}.

In XPath, it works the same way with nodes. select="foo|bar" means to use the
union of the node-set {all child::foo elements} and the node-set {all
child::bar elements}, producing the node-set.

Note that I'm mixing notations here; there are no curly braces in XPath, and
in XSLT they are only used in XSLT Attribute Value Templates to delimit XPath
expressions embedded in literal attribute values.

Mike

-- 
  Mike J. Brown   |  http://skew.org/~mike/resume/
  Denver, CO, USA |  http://skew.org/xml/

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