[tex4ht] [bug #278] Wrong mathml with $\langle$

Hans Georg Schaathun hg at schaathun.net
Thu Mar 31 20:53:04 CEST 2016

On Thu, Mar 31, 2016 at 10:51:23AM -0700, William F Hammond wrote:
> I think the source is nonsense -- or, at best, ambiguous -- if translation
> to HTML with MathML is envisioned.  For example, is this an abuse of math
> because the user does not know about \textless or how to obtain U+2329?  If
> it's indeed intended as math, is this an attempt to use \langle (U+27E8) as
> an ordinary math symbol other than a group opener?  Or is it intended to be
> the empty group properly marked up with
> "\left\langle{}\right." ?

I am not sure if I should take the question personally, or generally.
But since my question probably triggered the issue, I'll put in two
pennies on each account :-)

My use of the \rangle/\langle is to bracket e-mail addresses, i.e.
$\langle$foo at bar.invalid$\rangle$.  I totally agree that this is crap
as semantic markup, but it typesets rather nicely.  

The use is a habit which predates the ubiquity of unicode, and I have
never bothered to identify the corresponding unicode character or checked 
if that would work directly in TeX.

I think it is safe to assume that someone who wants \textless without
knowing the macro, would use $<$ rather than $\langle$.

> It's not clear what a sensible translation should be.

I also do not know what a sensible translation should be, but two points
should be noted.  Firstly, TeX was never designed for semantic markup,
and enforcing new semantics on macroes is not a good idea if it can
be avoided.  Secondly, mathematical symbolism is neither static nor
universal, except for a very small core.  \rangle and \langle may not
be the most probably candidates to be redefined for an ad hoc purpose,
but given the number of mathematicians and many narrow branches of the
field, /someone/ is surely going to do just that at some point.

I do not know much MathML myself, but I would not be surprised if a
sensible and consistent translation is impossible.  I would not
mind giving up my own peculiar use of the macros when I need to make
an OpenOffice conversion.  However, there will be valid uses.

:-- Hans Georg

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