gail currently only exports a very small number of interfaces, in libgail-util,
and currently, gailwidget.h. These interfaces are provided specifically so that custom widgets can more easily and consistently implement the ATK interfaces.

In general we don't want to export the other gail headers, since the
implementation details of how ATK is provided for specific widgets is not
something we want to require bincompat for, nor do we want these interfaces, in
general, to be used externally (other than the ones in libgail-gnome).

However, gailrenderercell is a class with virtual elements:
   * update_cache
   * property list

Each concrete gailrenderercell (gailtextcell, etc.) on gail implements or define these in a proper way.

If you want to define your custom cellrenderer, the proper way to implement his accessibility, is extend gailrenderercell and redefine this elements. If you want to do that, you require to access to gailrenderercell.h, but at this moment this .h is private.

This problem can't be solved using:
http://developer.gnome.org/projects/gap/presentations/GUAD3C/making-apps-accessible/anonymous-inheritance-1.html

This bug is similar to the bug 363128 (the begining of this description is an Copy&Paste :) ) but IMHO are different bugs, as the problems are slighty different, although the solution is very similar.