It is possible to define new classes - in fact, the WOM compiler
treats *.wom files as implicitly defining a subclass of the
built-in class Page. This feature is still under development.
It is intended for situations in which one wants to define a collection
of data items, e.g. a complex number or a salary record, associating
with this one or more ways of displaying it as HTML.
One can also define subclasses of built-in or user-defined classes, giving them new attributes or further constraining their behaviour.