glade_text_button_get_type

[丁少衡 <dshbusiness gmail com>]

Hello all,
I am reading the code about glade. The source code I use is glade-3.10.0. When I was reading the parts about it plugins(in the glade-3.10.0/plugins/gtk+/), I found some functions claimed but not implemented.
For example, in the file glade-3.10.0/plugins/gtk+/glade-text-button.h(c), there is a function named glade_text_button_get_type(), which returns a GType value.
What's the meaning of that? Could anyone help me?
Thanks.
dingshaoheng