[topicmapmail] Superclass-subclass indentation in the Omnigator

[Martin Bryan]

Jack Park pointed out

>For the constraints on the usage of <instanceOf>, see the description of
the element types that can be its parent:  <topic>, <occurrence>, and
<association>.

and asked:

>I wonder if it might be possible for this group to find some consensus
definitions wrt knowledge representation as practiced by the topic maps
community.

I wonder whether the rule should not be along the lines that <instanceOf>
should only apply to occurrences and associations while we introduce
<subclass> as the way of describing the relationships between topics.
Remember that topic maps already has a distinction between instances
(occurrences) and sets of discussable instances (topics). We should seek to
preserve this distinction as far as possible, and make it work for us.

Martin Bryan