Used to allow conditional content construction to be made streamable. Outputs the enclosed content only if the containing sequence also generates "ordinary" content.
The instruction can appear anywhere in a sequence constructor (and more than once). The content is output in the appropriate place among "ordinary" output.
Although intended primarily to make streaming applications easier to write, the instruction can also be handy irrespective of streaming to avoid evaluating complex conditions more than once.
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element
Notes on the Saxon implementation
New in XSLT 3.0, and implemented since Saxon 9.7.
The following code generates a header and footer only if there is content,
however it is not guaranteed-streamable because it processes child
item-for-sale elements more than once:
To make this streamable, it can be rewritten using the