[patch] improve internals documentation for nested function descriptors

[Eric Botcazou]

> This is precisely what I found so confusing about the original text.  To
> me, "custom" implies that the back end is *customized* to have its own
> descriptor implementation to conform to target-specific ABI standards,
> not that it uses a generic implementation in common code.

To me, "custom" sounds contradictory with "conform to" in this sentence.

And I don't follow your interpretation, back-ends are by definition customized 
to follow external constraints and not every macro/hook has "custom" in it.

> I could make the docs say both things, but from the perspective of a
> back end implementor, being explicit that it's a bit mask used to
> differentiate descriptors from any valid function pointer (so you can
> figure out what an appropriate value to define it to is) is more
> critical than describing what target-independent code does with a
> descriptor once it has identified that's what it's got.

Fair enough.

-- 
Eric Botcazou