Guide should say what characters are valid in variant names

[ryandesign@…]

Variant names may not contain a hyphen. (For example: "variant no-x11" would be wrong.) Underscores should be used instead (e.g. "variant no_x11"). The guide should mention this in the section on writing portfiles.

[markd@…]

I made modifications in #33664, #33665, and #33666. I'm closing the ticket, but feel free to critique the mods and reopen to make further suggestions if you like. There is always room for improvement. Thanks for catching this!

[ryandesign@…]

Thanks for your quick response!

But actually, rather than just mention that the hyphen is invalid, let's mention what is valid. All our ports' variant names right now use just the letters A-Z and a-z, numbers 0-9 and the underscore, so I think that's the list of valid characters we should publish in the guide. It's still worth mentioning specifically that the hyphen is invalid, since people seem to want to use that, and a handful of ports' variant names still use the hyphen; I'll work with those port maintainers to remove those.

Related: port lint should warn on illegal variant names; see #14147.

[markd@…]

Okay, take a look at r33774 and r33775 and see how that looks.