     |
Co-Constraints (DTD)
DTDs don’t support co-constraints:
<!ENTITY biblio.class.attribute "
class (doi|isbn|issn|libraryofcongress
|pubnumber|uri|other) #IMPLIED
otherclass CDATA #IMPLIED
">
The desired semantic is:
-
If class is “other”, then otherclass must be specified, otherwise
-
The otherclass must not be specified.