xinclude processing and XProc

test-suite sparked my mind on what effects xinclude may have during
processing of an XProc document.

There maybe times when you would want to give the pipeline author a
chance to specifically disallow xinclude processing (and have
implementator handle this)...perhaps a flag on pipeline?

also, thinking about the knock on effects of using xinclude within
p:inline elements.

thoughts?

Jim Fuller