processor switches

I know that W3 tends to avoid specifying any technology at this
level....but there are times with XSLT processors, and other
processors that I wished I could invoke processor switches (typically
invoked from commandline) at markup level.

for purposes of xproc perhaps we could consider a standard input port,
which could bring in name/value pairs in a simple XML document (could
leave this level of detail to implementator)

thx, Jim Fuller