Pverlay development documentation

[Geoff Swan <gswan3@bigpond.net.au>]

I have a need to write an overlay (openldap-2.4.44) and wondered if
there was any documentation for overlay development?
I have examined the sources in contrib/slapd-modules/ and was hoping to
locate something a bit more descriptive and maybe any must-do's and
gotchas for development.

>From a development environment perspective, is it advisable to use the
contrib/slapd-modules/ as a build location, using a Makefile based on
one of the existing overlays and also the non-exposed header files (eg
"portable.h") or not?

- Geoff