Hello,

	Sorry for the late response, I was hoping someone else would answer before I
	could, we are not that many but there are still a few very good guile-gnome
	users out there ... :)

> Pango attributes are instances of class <gw:wcp> in Guile-Gnome but they 
> are not GOOPS instances (i.e. (instance? x) returns false). Class name 
> <pango-attribute> is not defined at all.

Indeed, pango attributes are opaque pointers, in the manual you see:

	Class: <pango-attribute>
	
	Opaque pointer.

	This class defines no direct slots.

Note that the manual is automatically generated, which is why you read 'Class:
<pango-attrobute>, but on the next entry you can also read 'Opaque pointer', which
is an indication for users that the class has not been 'optimally' wrapped:

	they are not goops classes - subclass of <gobject>, such as <gtk-window>,
	they are (G-Wrap) opaque pointers.

In the manual, references to <pango-attribute> means it wish to receive an opaque
pointer of the corresponding attribute  ... and these are returned by the interface
creating pango attributes:

	pango-attr-size-new, pango-attr-font-desc-new ...

Opaque pointers are low level G-Wrap beats, so you don't want to involve yourself
there :). Their printing representation miss leaded you to believe they are
instances of ... which is not the case. When you create an attribute:

	scheme@(guile-user)> (pango-attr-size-new 10)
	$3 = #<gw:wcp <pango-attribute> 0x562572ca8c40>

	in the above, gw:wcp stands for 'g-wrap:wrap C type', and what you read is
	just an opaque pointer printing representation for  (pango-attr-size-new 10)

Just for info, below is a copy ot the automatically G-Wrap generated definition for
pango-attr-size-new [1]

> How can I test if an arbitrary  object belongs to some specific <gw:wcp> class,
> e.g. if an object is a Pango attribute?

You can't, you have to use their creator interfaces and attribute list operators ...

	scheme@(guile-user)> (pango-attr-list-new)
	$2 = #<<pango-attr-list> 562572e2f260 [native]>
	scheme@(guile-user)> (pango-attr-size-new 10)
	$3 = #<gw:wcp <pango-attribute> 0x562572ca8c40>
	scheme@(guile-user)> (pango-attr-list-insert $2 $3)
	scheme@(guile-user)> 

HTH,
David

[1]

{
  const char *gw__tmp1217_arg_types[1];
  static GWTypeSpec gw__tmp1218_arg_typespecs[] = { GW_TYPESPEC_CALLER_OWNED,  };
  gw__tmp1217_arg_types[0] = "int";
   gw_wrapset_add_function(gw__tmp0_c_info, pango_attr_size_new, 1, 0, "<pango-attribute>", GW_TYPESPEC_CALLER_OWNED, gw__tmp1217_arg_types, gw__tmp1218_arg_typespecs, "pango-attr-size-new", NULL, GW_FUNCTION_FLAG_LEAVE_RUNTIME);
}