button-press-event and button_press_evnet

["Zhibin.Guan" <zhibinguan 163 com>]

what is the difference between button-press-event and button_press_event??
I am reading the FAQ about gtk+-2.0 and look at the segment "how do I
catch a double click event"
In its example program, it use the signal "button_press_event",
but I substitue "button_press_event" with "button-press-event", it still
can works.

but I want to know what is the difference between button-press-event and
button_press_event??