RE: lax matching is not a great default behavior

[Drew Adams]

> > I mentioned "ad hoc" character equivalences because I didn't
> > think that the quotation-mark equivalences we've added are
> > included in any of the Unicode equivalences (whether
> > "canonically equivalent" or "compatible").
> 
> Indeed, we added equivalences for quote characters that are not
> defined by Unicode database.  I think that these equivalences should
> just be the initial value for the user-customizable part of the
> feature.  And I don't think these few additions justify new
> terminology, the existing one still describes even that.

Good.  We agree on both counts.  (1. The current, predefined
ad hoc equivalences should be an initial value for a user-defined
ad hoc equivalence group.  2. "Character folding" is fine for
describing all of this functionality.  Our use of the term
need not be limited to what the Unicode standard defines as
character folding.)

Wrt user-customizable: I would like to see (after 25.1, no
doubt) the design accommodate users easily defining their own
equivalence groups (not just a single defcustom for all ad hoc
equivalences).

And we can try to make it easy for them to [en|dis]able any set
of such equivalence groups selectively, including for different
contexts/modes.