XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (47 page)

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Authors: Michael Kay

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If the value of an attribute of a literal result element contains curly braces (
{
and
}
), then it is treated as an
attribute value template
(discussed further in the next section). The text between the curly braces is treated as an XPath expression, and is evaluated as a string; the attribute written to the result tree contains this string in place of the expression. For example, suppose we apply the following template to the
books.xml
file used earlier:

Because the
position()
function takes the values 1, 2, 3, and 4, as we move through the set of books, the output will take the following form:

Sayings of the Century

Sword of Honour

Moby Dick

The Lord of the Rings

It is also possible to generate attributes for a literal result element by two other mechanisms:

The attribute can be generated by an

instruction. This instruction does not need to be textually within the content of the literal result element in the stylesheet, but attributes generated in the result sequence must appear before any child nodes (elements or children).
The reason for this rule is to allow the XSLT processor to avoid building the result tree in memory. Many processors will serialize XML syntax directly to an output file as the nodes are generated, and the rule that attributes must be generated before child elements or text nodes ensures that this is possible. Technically, it's not the order in which the instructions are evaluated that matters (that's up to the implementation); rather, the rule is that attribute nodes in the result of evaluating a sequence constructor must appear earlier in the sequence than nodes to be used as children.
A collection of attributes can be generated by use of a named attribute set. The literal result element must contain an
xsl:use-attribute-sets
attribute that names the attribute sets to be incorporated: these names must correspond to

declarations at the top level of the stylesheet. The named attribute sets each contain a sequence of

instructions, and these cause attributes to be added to the generated element as if they were present directly in the content of the literal result element. Named attribute sets are useful to maintain a collection of related attributes such as font name, color, and size, which together define a style that will be used repeatedly in the output document; they are a direct parallel to the styles found in simpler languages such as CSS.

Attributes are added to the generated element node in a defined order: firstly, attributes incorporated using
xsl:use-attribute-sets
, then attributes present on the literal result element itself, and finally attributes added using

instructions. The significance of this sequence is that if two or more attributes with the same name are added, it is the last one that counts. It doesn't mean that they will necessarily appear in this order when the result tree is serialized.

Namespaces for a Literal Result Element

The namespace nodes of a literal result element are also copied to the result sequence of the sequence constructor. This is often the source of some confusion. The literal result element in the stylesheet will have a namespace node for every namespace declaration that is in scope: that is, every
xmlns
or
xmlns:*
attribute on the literal result element itself, or on any of its ancestor elements in the stylesheet. The only exception is that the attribute
xmlns = “”
does not act as a namespace declaration, rather it cancels any earlier declaration for the default namespace.

XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (47 page)

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