The "user level" documentation for gtk+ doesn't really exist. Specifically
I was looking for the following information:

 - format of the .gtkrc file
 - how to install themes, and theme engines

As it turns out I have found the desired info in the documentation of
"Resource Files" - but at first glance this documentation appears to be of
a technical nature only and I assumed that it was all about functions for
parsing configuration files (in the index, it is described as "routines for
handling resource files").

Basically what I am trying to say is that if a user is looking for the sort
of info I was looking for, it should be easier to find - it should not be
mixed up with the developer docs and the first thing they see should
definitely not be a C-header synopsis.