No diffs in diffpdf "words" mode; two expected line-breaking diffs in "appearance mode" for the C++ 20nn non-breaking space.

I can squash some of these commits if desired.

I stole a few commits I liked from this PR. Please rebase.

Rebased.

After @tkoeppe's partial merge, the remaining change is to morph blah\opt into \opt{blah}.

Is the "C++ 2003" change worth it? Either we already don't break the line, or if we need to break, it doesn't look like a terrible place to break. Why prevent the line break at all costs?

@tkoeppe: That's why it is a separate commit.

In my view, it's somewhat ugly to have "C++" at the end of a line and then have the next line start with "2003". And in the two situations where it makes a difference, TeX finds another linebreak opportunity. Maybe it's better to apply some extra penalty as opposed to "prevent at all costs", though.

Yes, if we could "discourage" rather than "forbid absolutely", that'd be nice. I.e. it's good if we can improve the situation without breaking it.

Dropped patch for avoiding line breaks for earlier versions of C++.

@zygoloid : This merge went the wrong way: You merged "master" into my branch, it seems, rather than the other way round.

@jensmaurer: No, I think he was trying to rebase your PR. Apparently that's a thing you can do now.

@tkoeppe: Ahem. I thought "rebases" don't want to do a "merge", but a force-push, to keep the history tree clean?

Ah, the \tilde changes. Let me fix those in a proper rebase and push again.

No visual diff, looks good. Will leave to @zygoloid to merge because of the wide impact.