saxon:asynchronous
This attribute may be set on the xsl:result-document instruction. The default for
Saxon-EE is yes, which causes the instruction to be evaluated in a separate
thread, if there is a spare thread available (the maximum number of threads used is
configurable using RESULT_DOCUMENT_THREADS).
A possible reason for setting the value to no is that the stylesheet calls
extension functions with side-effects, where it is important for the calls to be in the
right order.
Asynchronous processing of xsl:result-document is automatically suppressed if
tracing (using a TraceListener) is enabled.