xsl:fork
The result of the xsl:fork instruction is the sequence formed by
concatenating the results of evaluating each of its contained instructions, in
order.
Category: instruction
Content: (
xsl:fallback*
, (
(
xsl:sequence
, xsl:fallback*
)*
| (
xsl:for-each-group
, xsl:fallback*
)
)
)
Permitted parent elements:
any XSLT element whose content model is
sequence-constructor; any literal result element
Element has no attributes
Notes on the Saxon implementation
The instruction is pointless when not streaming, but it is still supported.
Fully implemented since Saxon 9.7. Streaming of
xsl:for-each-group, as a child of xsl:fork, with a
group-by attribute was introduced in 9.7 maintenance releases and
is fully supported in Saxon 9.8.
In Saxon 9.6, the instruction was implemented with restrictions: specifically,
the content of xsl:fork must consist of a sequence of
xsl:sequence instructions, and can not include
xsl:for-each-group elements.
The Saxon 9.6 implementation of xsl:fork in streaming mode does not
actually use multiple threads: rather, the events notified by the XML parser
(such as startElement and endElement) are notified to each prong of the
xsl:fork in turn. Each prong accumulates its result in a
temporary tree held in memory, and these temporary trees are combined on
completion. The instruction is most effective when each prong consists of a call
to xsl:result-document; in this case the output can immediately be serialized,
leaving no temporary data in memory.