We all run in php-gtk site to seek documentation for different methods or classes but often there is no helpful description there. Also the try and error approach is not always what you want if you are in a hurry.
Fortunately you can use other web sites that refer to gtk for other languages in order to get help.
For example here: http://www.pygtk.org/docs/pygtk/class-gtktextiter.html#method-gtktextite... I found information for the "forward_visible_word_end" method. So if you are careful most times (given the same gtk methods are available for other languages too) you can find help using other sites, no matter if that site is about gtk (the same goes for cairo) for c++, python etc.