About the splitting...

I've been thinking about splitting the specification in two, and as far as I
can see, this is already discussed in the WG.

So, my comments about it. I'd think splitting is a good idea, but not with
the optional steps being in the second. Instead, I'd suggest having the
whole standard step library as a separate document and the XProc framework
(or "core") steps to remain in this document.

Regards,
Vasil Rangelov