Any dictionary will quickly show that this usage of "active" is
well-known. From dictionary.reference.com:
2. being in a state of existence, progress, or motion:
5. characterized by action, motion, volume, use, participation,
etc.: an active market in wheat; an active list of
reference.com doesn't mention it, but biology and biochemistry have a
very similar usage, viz. "active receptors", "active sites".
> "Active" is the wrong word. Possibly "Reactive" would be a
> suitable one - a "reactive region" being one which reacts to
> commands directed at it.
I don't think that's as good a term as "active". The region is not an
object with methods it uses to "react" to commands. It is an object
to which things may be done, unless it is inactive. "Receptive
region" might be more accurate, but unfortunately there is no verb "to
receptivate". I think documenters would mutiny if they had to write
"to activate the receptivity of the region".
> Do you have definitions of (as contrasted to a discussion around)
> "active region" and "active mark" that you could contribute to the
> Emacs manual?
Not really. As you say, transient-mark-mode is complex. And we've
been through this discussion before, IIRC, and the XEmacs terminology
was considered inappropriate for Emacs.
To recap, XEmacs does not have a concept of "active mark" (or if that
term is used, I guess it is identical to "the mark", ie, the mark on
the top of the mark stack). It does have two concepts of active
region, the more often used of which is `region-exists-p' (for
compatibility with code written for Emacs):
Return t if the region exists.
If active regions are in use (i.e. `zmacs-regions' is true), this
means that the region is active. Otherwise, this means that the
user has pushed a mark in this buffer at some point in the past.