[luatex] "Proper" use of \Udelimiterover &c

[Taco Hoekwater]

Hi,

On 07/14/2010 08:49 AM, Will Robertson wrote:
> Hi,
>
> Just checking that I'm using these primitives correctly.
>
> Plain & LaTeX have some complex alignment definitions for \overbrace and
> friends; am I correct in thinking that \Udelimiterover are designed to
> replace all of that?

Yes.

> Khaled's minimal example is:
>
> \input luaotfload.sty
> \font\4={name:XITS Math:mode=base;script=math} at 10pt
> \textfont4=\4
>
> $$
> \Udelimiterover "4 "23DE {a+b}
> + \Udelimiterunder "4 "23DF {a+b} = C
> $$
>
> But here the spacing is much too large between the delimiter and its
> contents. Am I supposed to be boxing up/smashing/whatever the argument
> myself?

No, you are doing it right. Whether *I* am doing it right is a
different question. Ulrik, can you try this overbrace stuff in
Word to see how it looks?

> If not, and it's just a matter of setting the delimitervgap
> appropriately, I'm curious why (philosophically) the \mathop{...}\limits
> construction is required:

> \Umathoverdelimitervgap\displaystyle=-3pt % ?
> $$
> \mathop{\Udelimiterover "4 "23DE {a+b}}\limits^{d+e}
> + \Udelimiterunder "4 "23DF {a+b} = C
> $$
>
> Would it make sense to treat a \Udelimiterover construction as an
> operator with limits automatically? E.g., I expected
>
> {\Udelimiterover "4 "23DE {a+b}}^{d+e}
>
> to do the "right thing", but looking at it this way perhaps it's
> impossible to do this with this construction of maths primitives? (Sorry
> I'm not entirely up to speed on the internals of the maths engine.)

When I implemented this, I did not realise that this would make sense.
Is such a construct as this *always* a large operator?

Best wishes,
Taco