Specialization: wholes in class attribute

manolson <ext-auriel.n.manolson@...>

if dtd A specializes dtd B.
- should all elements in A only specialize elements of B,
- or may they specialize any element in any package which A
If package Z specializes package Y which specializes package X,
should all elements in Z specialize elements in Y, or can they
directly specialize elements in X ?

Must all words within the class attribute refer to elements that
actually exist (and are defined for) the said package:

For example, is the class attribute for element ezysect in package
ezyref: "- tipic/section whyref/section ezyref/ezysect" valid even if
there is no such element in package whyref with the class attribute "-
tipic/section whyref/section"

I would think that wholes (in either respect above) would not be
allowed in the class attributes in order to comply with the DITA standard.

Are there clear rules about this?
(apologies if I have missed these somewhere)