Where's the line between "extension" and "development"?

I am thinking about moving chapter 34 (Index Cost Estimation Functions)
and section 33.9 (Procedural Language Handlers) out of Part V (Server
Programming) and into Part VII (Internals), on the grounds that
they are only of interest to hard-core developers. The other stuff in
Server Programming is of use to mere mortals who just want to get
their work done, but these sections don't seem to be addressing the
same audience. In particular it seems weird that documentation on how
to write a new procedural language comes before any of the documentation
on how to use the existing PLs.

I'm also inclined to push chapters 36 (Triggers) and 37 (SPI) to the end
of Part V, after the chapters on procedural languages, because these
two chapters are only of interest to authors of C-language functions.
This would help maintain the general structure of the part: simpler,
easier-to-use stuff before advanced stuff.

Comments?

regards, tom lane