noob question: g_signal_connect()

[Christopher Howard <christopher howard frigidcode com>]

Hi. I've installed the api documentation from the source code for both
gtk+ and glib, but I can't seem to find an api description of
g_signal_connect(). The examples I usually see are along the lines of

code
----------
  g_signal_connect (G_OBJECT (button[0]), "draw",
                  G_CALLBACK (draw_callback), NULL);
----------

Could somebody please explain two things:

1) What is the purpose of the string in the second position in the
parameter list?

2) What is the purpose of the fourth parameter slot, with the NULL in
it? Can other options go there?

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