XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (384 page)

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Authors: Michael Kay

BOOK: XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition
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Don't make the mistake of thinking that if
$n
holds the string
“title”
, say, then
./$n
means the same as
./title
. Variables in XPath represent values, not parts of an expression. To select the child elements whose name is in
$n
, use
*[name()=$n]
.

Examples of the Binary
/
Operator

The following examples illustrate that although axis steps are often used as operands of
/
, any kind of expression is legal:

Expression
Description
descendant::para/@style
In this example both operands are axis steps. The first step selects the descendants of the context node that are

elements; the second step uses the abbreviated syntax
@style
, which is short for
attribute::style
, and selects the
style
attributes of these elements.
section[1]/clause[3]
In this example each of the operands includes a positional predicate. The first step selects the first

element that is a child of the context node, the second
Step
selects the third

element that is a child of the selected

.
chapter/section/para/sentence
This path expression selects every

element that is a child of a

element that is a child of a

element that is a child of a

element that is a child of the context node. The expression can be decomposed into a nested set of expressions each of which uses a binary
/
operator:
((chapter/section)/para)/sentence
.
doc(‘a.xml’)/id(‘Z123’)
This example illustrates that the operands of the
/
operator do not have to be
AxisStep
expressions. This example selects the document with a particular relative URI, and using the resulting document node as the context node, then selects the element with a particular ID value.
book/(chapter|appendix)
This is another example that uses an operand that is not an
AxisStep
. For each selected

element, it evaluates the expression
(chapter|appendix)
, which selects all the child

and

elements of the book, in document order.
$chap/title
Using a variable reference on the left-hand side of
/
is very common in
for
expressions, which we will examine in Chapter 10. A typical example is
for $chap in //chapter return string-length($chap/title)
. This kind of construct is even more common in XQuery.

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