Gtk::Editable::on_insert_text

[Antonio Coralles <noche suapie reflex at>]

I just was thinking about the most elegant way of restricting the chars 
a user can enter into a Gtk::Entry. At first i thought I should do that 
by overriding on_changed() but then, after looking at the dokumentation 
for Gtk::Editable the functions

virtual void  insert_text_vfunc (const Glib::ustring& text, int& position)
virtual void  on_insert_text (const Glib::ustring& text, int* position)

caught my attention. The problem is that these functions are completeley 
undocumented - especially I don't understand what i should do with int& 
/ int* position - what happens when i change the value of 
position/*position ? Are these functions at least suitable for my 
purpose ? Should i call [when overriding] the base class routines if i 
want a char to be accepted and avoid that if i don't want that ?

Thanks,
               Antonio