setQdata
Sets an opaque, named pointer on a #GParamSpec. The name is specified through a #GQuark (retrieved e.g. via g_quark_from_static_string()), and the pointer can be gotten back from the @pspec with g_param_spec_get_qdata(). Setting a previously set user data pointer, overrides (frees) the old pointer set, using null as pointer essentially removes the data stored.
Parameters
quark
a #GQuark, naming the user data pointer
data
an opaque user data pointer