What are valid characters in an X11 .conf Identifier name? Where can I find what characters are valid in an X11 config file `Identifier` name? I'd like to name my identifier `libinput touchpad disable tap-to-click` but I don't know if hyphens are valid. I'm running Manjaro Linux.

I don’t think there are any particular restrictions, apart from the use of quotes; the configuration file manpage doesn’t mention anything specific. Looking at the parser source code, a string can contain anything apart from double quotes, carriage returns, newlines and the null byte.

You should certainly be able to use hyphens.