This manual was originally a plaintext to HTML conversion of the even older GTKeyboard manual that came with the program. It has since been converted to LATEX format and should be available in a variety of other formats. I've tried to mention just about everything, but I'm sure there are things that I missed.
If you would like to report some feature documentation missing that you'd like to see, suggest another subtopic, correct my spelling or grammar, please email me at s2mdalle@titan.vcu.edu and I'll clear it up as quickly as possible. If you would like to write a section, go for it, and I'll incorporate it as long as it's relevant to GTKeyboard.