DECLARE_SCHEME_CALLBACK (width, (SCM));
DECLARE_SCHEME_CALLBACK (height, (SCM));
DECLARE_SCHEME_CALLBACK (pure_height, (SCM, SCM, SCM));
DECLARE_SCHEME_CALLBACK (width, (SCM));
DECLARE_SCHEME_CALLBACK (height, (SCM));
DECLARE_SCHEME_CALLBACK (pure_height, (SCM, SCM, SCM));