xsl:for-each

Causes iteration over a specified sequence of items.

Category: instruction
Content: ( xsl:sort* , sequence-constructor )
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element

Attributes

select

expression

Defines the sequence of items over which the statement will iterate. The XSLT statements subordinate to the xsl:for-each element are applied to each item in the input sequence in turn. The full syntax of expressions is outlined in XPath Syntax.

array?

expression

Experimental addition in XSLT 4.0, allowed only if syntax extensions are enabled: an alternative to the select attribute. Defines an array over which the statement will iterate. The XSLT statements subordinate to the xsl:for-each element are applied to each member of the input array in turn; the members are presented as instances of the type record(value), which can be converted to a sequence (or in many cases, a single item) using the expression ?value.

map?

expression

Experimental addition in XSLT 4.0, allowed only if syntax extensions are enabled: an alternative to the select attribute. Defines a map over which the statement will iterate. The XSLT statements subordinate to the xsl:for-each element are applied to each entry of the input map in turn (in an undefined order); the entries are presented as instances of the type record(key as xs:anyAtomicType, value as item()*), so the key can be obtained using ?key, and the value using ?value.

separator?

{ string }

Experimental addition in XSLT 4.0, allowed only if syntax extensions are enabled. The value is an attribute value template. If present, a text node is formed from the effective value of the attribute, and this text node is inserted into the result sequence after processing every item in the (sorted) input sequence other than the last.

saxon:threads?

integer

The items selected by the select expression of the instruction are processed in parallel, using the specified number of threads. Requires Saxon-EE. For details see saxon:threads.

Notes on the Saxon implementation

Saxon-EE offers an extension to the xsl:for-each instruction; the saxon:threads attribute allows the items in the input sequence to be processed in parallel. This is most likely to be effective when (a) the processing of each item is expensive, and (b) the output produced by processing each item is small. Allocating multiple threads when each item generates a new result document is pointless, because xsl:result-document already runs in a separate thread.

For xsl:for-each to be streamable, the W3C rules require that the select expression must be "striding", which essentially means that it may use the child axis but not the descendant axis (to ensure that selected nodes do not overlap each other). Prior to Saxon 9.5, Saxon attempted to be more liberal than this, and allow limited streaming also when the descendant axis was used. Since Saxon 9.6, the implementation has been brought into line with the W3C specification. In many cases the restriction can be circumvented by using the outermost function, for example the expression outermost(//title) is striding even though it uses the descendant axis.

Details

The xsl:for-each element can be used as an alternative to xsl:apply-templates where the child nodes of the current node are known in advance.

It may have one or more xsl:sort child elements to define the order of sorting. The sort keys are specified in major-to-minor order. The expression used for sorting can be any string expression. The following are particularly useful:

Examples

Example 1

<xsl:template match="BOOKLIST"> <TABLE> <xsl:for-each select="BOOK"> <TR> <TD><xsl:value-of select="TITLE"/></TD> <TD><xsl:value-of select="AUTHOR"/></TD> <TD><xsl:value-of select="ISBN"/></TD> </TR> </xsl:for-each> </TABLE> </xsl:template>

Example 2

Sorting with xsl:for-each. This example shows a template for a <BOOKLIST> element which processes all the child <BOOK> elements in order of their child <AUTHOR> elements.

<xsl:template match="BOOKLIST"> <h2> <xsl:for-each select="BOOK"> <xsl:sort select="AUTHOR"/> <p>AUTHOR: <xsl:value-of select="AUTHOR"/></p> <p>TITLE: <xsl:value-of select="TITLE"/></p> <hr/> </xsl:for-each> </h2> </xsl:template>

Links to W3C specifications

XSLT 2.0 Specification

XSLT 3.0 Specification

See also

xsl:apply-templates

xsl:sort

saxon:threads