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 FeatureKeys.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.