Each RET text has several potential hierarchies, both bibliographical and generic. Critics see many other structures in texts, based on genre-related assumptions, and these are perhaps subject to more disagreement than bibliographical organization, which arises from a factual study of the physical nature of a book or manuscript. However, even the top-down hierarchies implicit in RET encoding can be reasonably questioned. Under some circumstances, a reader may well believe that the entire book is contained in the line being read.
Any hierarchy is an interpreted thing.
There are certainly too many questions about how any playwright handles these units to propose one general hierarchy for plays, as TEI does. Such command files belong to technical writing, in which precision and lack of ambiguity are desirable and feasible. Under some circumstances, this appropriation of an author's rights makes sense. DTDs, of course, have some limitations. They can only recognize a maximum of two parallel structures in a text and can only use one of those structures at a time.