Re: Dash in regexp character classes: Beginnig vs. end [was: Use the characters "+" and "-" in regular expressions]

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Thu, 20 May 2021 09:15:29 +0200, "tomas@tuxteam.de" <tomas@tuxteam.de> said:

    >> I quoted this from (elisp) `Regexp Special':
    >> 
    >> To include a ‘-’, write ‘-’ as the first or last
    >> ^^^^^^^^^^^^^
    >> character of the character alternative, or as the
    >> upper bound of a range.  Thus, ‘[]-]’ matches both
    >> ‘]’ and ‘-’.
    >> 
    >> That's from Emacs 26 (and all prior releases, at least
    >> as far back as Emacs 20).  But yes, they changed that
    >> text for Emacs 27, to this:
    >> 
    >> To include ‘-’, put it at the end.
    >> ^^^^^^^^^^
    >> ___
    >> 
    >> For Emacs 20, it says this:
    >> 
    >> To include a `-', write `-' as the first or last
    >> character of the character alternative, or put it
    >> after a range.  Thus, `[]-]' matches both `]' and
    >> `-'.

    tomas@tuxteam> Oh. That is interesting. Anyone knows why that change?

It makes the description and usage simpler and more regular, and less
error-prone.

Since I never remember the rules for this stuff anyway, I do this
instead:

(rx (or ?- ?+ ?.))
=> "[+.-]"

but of course parenthesis-like characters still need to be escaped:

(rx (or ?\) ?\] ?-))
=> "[])-]"

Robert
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