List of Keywords/variables allowed in .conf files

Is there a list of the current supported variables/keywords in the .conf files. I am working on an interface to work with these files and I can’t find a list. I have been digging through the chan_sip.c and other related source files but this seems like a hit and miss solution. I am hoping that there is a list out there. I have been through the voip-info.org web site and found what is there but the documentation on this issue seems to be out of date and not complete.

The configuration files in question are:

sip.conf
iax.conf
mgcp.conf
skinny.conf
h323.conf

avoteam, did you found a list of supported variables/keywords?