Re: [MathML4] Deprecation/Removal of the mfenced element

Le 26/07/2016 à 21:11, Daniel Marques a écrit :
> I also like the "mfenced". Vertical stretchies with <mo> are difficult to
> understand from the point of view of someone who uses a formula editor.
> What people understands when editing is that an open and close parenthesis
> grows according to what's inside. Thus, for people who do editors, the
> preferred feature is the mfenced.
You can definitely use mfenced internally in a formula editor if that
improves the UI. However, if that editor is not able to import/export
from and to the canonical form described in the MathML recommendation
then that's definitely a big flaw in that product.

> There is also a VERY important aspect which is BACKWARD COMPATIBILITY.
> There are plenty of formulas that use mfenced. Both Microsoft Word and
> WIRIS (I'm not able to test MathType at this moment) use the mfenced tag
> for stretchy parenthesis.
>
> Losing backward compatibility will result that a lot of formulas stop
> working. This would yield a lack of trust on the MathML specification.
> Please do not commit that mistake!
MathML is not implemented in Edge or Blink, so we currently have to use
converters to other formats in order to display formulas in all web
rendering engines. Having programs to put MathML in a canonical form for
old documents before delivering to web engines is not worse in my
opinion. And there is already a lack of trust in the MathML
specification because not all browser vendors have shown interest in
MathML until recently, because some Math WG members and contributors
seemed more interested in a theoretical standard than to consider
concrete feedback from web engines developers, because the current
MathML specification is too vague to implement high-quality math
rendering or handle subtle rendering aspects and because the official
MathML test suite is not runnable in browsers' test framework in its
current form. The quick work done for the past few months on WebKit and
Blink at Igalia showed that by extending / cleaning up the MathML
specification and rewriting the test suite, things become much easier
for web engines developers to understand, implement and test and for
browser vendors to accept a proposal that integrates well in their code
base. The goal of the discussion is to (re?)open a constructive
collaboration with people involved in the MathML specification and with
web engines developers.

To come back to mfenced, it has always been the source of bugs in Gecko
and WebKit that have added maintenance cost. And it has been a burden
during our refactoring in WebKit: we have spent and continue to spend *a
lot of time* to avoid breaking the current support and this is as much
time that could have been spent on working on more important aspects of
the MathML implementation. So although there is no rush for removing
that support, we believe it is important to report this issue so that it
can be taken into account in the long term. As I said in the menclose
thread, with the new layout rules in Blink it's very unlikely that
WebKit's mfenced implementation can be accepted by Google reviewers and
we do not plan to try it.

-- 
Frédéric Wang