The documentation has been restructured to split out a brief summary
paragraph out from the following elaborating paragraphs.

I also attempted my hand at wording improvements and adding articles
where I felt them missing, but being non-native english speaker these
may need more thorough review.

They have been deprecated since commit 01ac5a97
which was part of the 1.49.0 release, so from the point of nightly,
11 releases ago.

There are cases, when data in the buf might or might not be an error.

`self.buf` can contain a surrogate, but only a leading one.

This makes `PartialOrd` consistent with the other three traits in this
module, which all include links to their respective mathematical concepts
on Wikipedia.

Just happened to notice this in passing

Analog to 9648b313 #93208

New implementation takes into account contents of `self.buf` and rounds
lower bound up instead of down.

`const_allocate`:  Returns a null pointer at runtime.

Closes #75017

aborting immediately.

The panic handler is called with a special flag which forces it to abort
after calling the panic hook.

allowed to trigger unwinding.