>Is it possible to
specify that if PLACEMENT does not exist, then the values for ALIGN
are as specified, but if PLACEMENT exists then the meaning of ALIGN
changes and its possible values also changes?
Yes, but as an application convention; it's not possible to enforce
it in SGML (unless you rewrite the whole structure and convert some
attributes to elements).
Terry Allen ([log in to unmask]), Online Books Editor, Songline Studios
affiliated with O'Reilly & Associates, Inc.
A Davenport Group sponsor. See http://www.ora.com/davenport/README.html
Footballisms: "They don't need to score per se on this possession."