"opt" should not be italicised

[tkoeppe]

I think the "opt" modifier we subscribe to grammar items should not be set in italics, since it is not itself a piece of grammar.

I would probably set it like a named math function, i.e. \operatorname{opt}.

[jensmaurer]

No objection from me, but that's probably not C++17 material.

[tkoeppe]

Sure. We should probably pick this up when we look at the xspace business (#1439).

[jensmaurer]

Editorial meeting consensus: Leave italics as-is.