Alex Shinn scripsit:

> You didn't give any justification for this conclusion.
> What's wrong with providing features?

For one thing, there is no way to do it.  If I write a portable
implementation that supports backreferences, how do I cause the existence,
or even the importation, of that package to assert the regexp-backrefs
feature?  After all, I might have several different implementations
lying about.

--
Principles.  You can't say A is         John Cowan <xxxxxx@ccil.org>
made of B or vice versa.  All mass      http://www.ccil.org/~cowan
is interaction.  --Richard Feynman