In thinking about Paul Rubin's new math modules, it occurred to me that
it would be nice to have some conditionals in the layout files. Attached
is a patch that adds IfStyle and IfCounter tags. The effect of these is
to act as normal Style and Counter tags do, if the style or counter
already exists; otherwise, the contents is read and discarded, as if it
were a big comment block.
So one can do things like this:
IfStyle Axiom
...
End
and thereby modify the style, but only if it exists. This will be useful
in modifying math environments: In some cases, we do not know exactly
what styles we have.
I think this will be sufficient for actual needs. But it's an obvious
question whether we should do something more general. I'd also
appreciate comments on the way I've done this.
By the way: Shouldn't Counters::newCounter() check whether the counter
already exists before it creates a new one?
Richard
