Types and operations
********************
NOTE: Names of element types, attributes and entities should be
treated as far as possible as a real type. In versions prior to 1.0
names are represented by lisp symbols but in 1.0 they are strings.
Perhaps I should make a `psgml-api.el' that defines some functions
to deal with names. Then it would be possible to write code that works
in both 0.4 and 1.0.