Does LCL support subtyping?

Strictly speaking, the ANSI C type system is pretty flat:
you have void *refany, struct _opaque *refT,
and struct { int x} *refRec.

But folks go through some contortions to simulate SmallTalk-like
objects; for example, Xt Widgets.

Is there any way to express the Modula-3 "<:" concept in LCL?

Perhaps this is supported in the C++ interface language, but I
can't seem to conjure up any info on that stuff. (The address
seems to be out of date.)