Re: [EXTERNAL] Re: Minutes: MathML Core meeting July 27, 2020

<mo> has a "form" attr. Its value can be prefix, infix, or postfix, where
prefix/postfix are used for open/close (i.e., fences). With well-structured
mrows, distinguishing between all the forms works via defaults if not
specified as their position in the mrow determines what is prefix (first in
the mrow), postfix (last in the mrow), and infix (anything else). If it
isn't well structured, the mo's *should* have the "form" attr specified.
Sadly, that doesn't happen that often in poorly structured MathML; but
separator/fence aren't specified much either. In those cases, you may get
suboptimal spacing and the semantics become murky (e.g "1 + | a | b | c | +
2").

Unicode has a number of different characters for vertical bars; finding
them is left as an exercise to the reader ;-)

    Neil


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On Mon, Jul 27, 2020 at 5:37 PM Deyan Ginev <deyan.ginev@gmail.com> wrote:

> Hello,
>
> I am trying to follow the discussion, and would love to ask for help
> with clarifying the terminology/use cases here.
> Paging through the TeXbook, it appears to me vertical bars are given
> three independent treatments - 1) simple symbol |, 2) middle fence,
> e.g. \middle|, \bigm| and 3) relation: \mid. I'm attaching a tiny PDF
> file that shows the (indeed visible!) differences between the four,
> when there is a proper 2D object to delimit.
>
> So, I think I am reading Murray's examples as if separator=true in the
> Dirac notation maps onto \middle|, i.e. "a middle fence", and
> fence=true for bra and ket maps onto \right| and \left|.
>
> As someone who had to learn the meanings of "fence", "separator" and
> "delimiter" as a second language, I will confess to having undergone
> some significant confusion in building a mental image where the three
> words aren't outright synonyms. In colloquial English it appears that
> fences were used very early on to separate fields, and hence delimit
> them. On the other hand, I will also confess I have never had any
> confusion with understanding "left", "middle" and "right" as distinct
> concepts.
>
> I think it's quite reasonable that the various uses of vertbar should
> be expressible in (normative) presentation MathML, as Murray suggests,
> so there should either be 1) an alternative representation with
> spacing/sizing directives, or 2) the a11y attributes would need to
> become normative (which is unlikely from what I understand), or 3) the
> status quo must be maintained.
>
> Greetings,
> Deyan
>
> On Mon, Jul 27, 2020 at 7:41 PM Murray Sargent
> <murrays@exchange.microsoft.com> wrote:
> >
> > The fence and separator attributes are useful in Dirac notation. For
> example, in the expectation value , the vertical bars are separators (not
> absolute-value fences), while in the bra , the vertical bar is a closing
> fence. So separator=“true” conveys the former and fence=”true” conveys the
> latter. Both LaTeX and OfficeMath have these distinctions, so it’s
> important that they don’t get lost in Presentation MathML.
> >
> > At some point, I’d like to offer the richness of OfficeMath on the web
> and MathML is the obvious storage format for that. So I really don’t want
> to deprecate MathML to the point where we can’t speak and display it
> correctly. An even more ambitious goal is to be able to compute with
> Presentation MathML, a goal that wants more attributes rather than less.
> Browsers need to be able to speak math correctly and so even if the display
> of a vertical bar is the same for absolute value and the expectation value
> above, it isn’t spoken the same way. So we need the distinction and should
> fix the description in the MathML spec.
> >
> > Thanks,
> >
> > Murray
> >
> >
> >
> > From: David Carlisle
> > Sent: Monday, July 27, 2020 3:58 PM
> > To: public-mathml4@w3.org
> > Subject: [EXTERNAL] Re: Minutes: MathML Core meeting July 27, 2020
> >
> >
> >
> >
> >
> > on fence= and separator=  the mathml3 spec says
> >
> >
> >
> > This attribute generally has no direct effect on the visual rendering,
> but may be useful in specific cases, such as non-visual renderers.
> >
> >
> >
> > I think the proposed semantic attributions would be giving much better
> non-visual clues here and suggest we just drop both of these from full
> >
> > (we could potentially keep them in the schema as legacy ignored
> attributes)
> >
> >
> >
> > David
> >
> >
> >
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> >
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