XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (295 page)

The reasoning behind these rules is that names of elements in the stylesheet use the standard XML default namespace
xmlns=“ ”
; names of elements in the source document use the special default
xpath-default-namespace
, and names of objects other than elements never use a default namespace.

A QName with no prefix appearing in an XPath expression never uses the default namespace defined in the source document.

It's a common mistake to forget this. Your source document starts as follows:

and your stylesheet starts:

Why doesn't the template rule for
match=“html”
fire when the

element is encountered? The answer is that the default namespace (declared with
xmlns=“…”
) applies to unprefixed
QName
s in the source document, but it doesn't apply to unprefixed
QName
s appearing in expressions and match patterns in the stylesheet. You either need to write:

or you need to define an
xpath-default-namespace
:

What's worse, your source document might actually not start with:

but rather with:

Here it's not obvious that the

element is actually in a namespace. But it is, because hidden away inside the DTD is the sneaky little definition:

which has the effect of adding the namespace declaration
xmlns=“http://www.w3.org/1999/xhtml”
to the

element whether you asked for it or not. This means that a bare
match=“html”
in your stylesheet won't match this element; you need to match the namespace as well.

Operators

There is no hard-and-fast rule about exactly what constitutes an operator in the XPath language; but this is a good place to provide a general overview of the different kinds of operator.

We can classify as first-order operators all the operators that take one or more expressions as their operands, and produce a result that is obtained by evaluating the operands, and combining the values of the operands in some way. The first-order operators are listed in the table below, in precedence order. Operators listed on the same row of the table have the same precedence.