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.
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.