The root documentation format is a sub-set of the format TEXI. TEXI is the de-facto standard documentation format of the GNU project.
The reason to use only a subset of TEXI is that the available TEXI2XXX converter tools did not create the needed formats and I have developed a special t2h.pl in few hours that created the special format that I found most appropriate. On the other hand this tool only accepts a subset of TEXI. If other commands, out of the sub-set are used the tool passes them to the output.
To accommodate the automation of inclusion of other files, parts of other files or program outputs the language Jamal is used. This is a macro language written in Perl. It is a bit slow, but elegant and most importantly allows you to write some macros in Perl. Thus the original format is TEXI/JAMAL which is converted to pure TEXI when processed with JAMAL.