Re: mfenced as a special case of mrow -- Was: angle brackets in math


Robert Miner writes in part:

> If I recall correctly, the separators attribute was introduced to
> accommodate things like hypergeometric function notations like
> [a,b,c;d] or bra-ket notations like <a|c>, and I think there were a
> number more like that.  I think I was the original proposer of the
> current syntax, and I wish I hadn't.  It was a blunder.  It's awkward
> to have a microsyntax for the attribute value, and there is no good
> way to say separators="" since one cannot tell from some DOM
> implementations whether the attribute is unset or it is set to "".  I
> think these cases are all handled better by the mrow notation.
> Speaking personally, I don't think mfenced is especially closely
> connected with lists, Maple's behavior notwithstanding.  Both the mrow
> and mfenced constructs are purely presentational and will be used and
> abused in all kinds of ways in practice. Any attempt to infer
> semantics from presentation has to deal with that, unless the context
> is restricted in some way, e.g. by Maple, or gellmu, or MathType, etc.

Robert may wish he hadn't proposed the original syntax, but I'm glad
he did.  It was a start in a good direction.

I think the version 3 draft should suggest that mfenced is to be viewed
as a list constructor.  It's pretty much what it already is given that
the values of "separators" should be separators.  Note in computer algebra
systems like Maple there is no presumption that list components are objects
of the same type, though often they are.

                                    -- Bill

Received on Saturday, 31 May 2008 19:57:07 UTC