how to read Gtk signal document ?

[KC <kcc1967 gmail com>]

Hi,

Could someone explain more detail about the following document for GtkButton

Signals

  "activate"                                       : Run First / Action
  "clicked"                                        : Run First / Action
  "enter"                                          : Run First
  "leave"                                          : Run First
  "pressed"                                        : Run First
  "released"                                       : Run First


I can guess what these mean, but can't find any official document for them.
Specially ... what does "Run First" mean ?
All of the above signal are labeled as  "Run First", so what's the real order ?
Thanks

Regards,
KC