Re: master 6eeab90632: Don't accept whitespace or hex floats in rgbi: colour specs

[Philip Kaludercic]

Po Lu <luangruo@yahoo.com> writes:

> Mattias Engdegård <mattiase@acm.org> writes:
>
>> It's bug#54263 -- sorry about the omission from the log message.
>
> Thanks.
>
>> So it might seem, but over-tolerant implementation is generally a
>> mistake. It restricts compatibility in the other direction (what
>> worked with Emacs won't work elsewhere)
>
> AFAICT, there are no other implementations of such an rgbi color
> specification (please correct me if I'm wrong.)

It seems the "rgbi" (that stands for RGB Intensity) syntax comes from
X11[0], specifically "XCMS" (X Color Management System) Interestingly
enough, if you look around you can find that the "rgbi" prefix seems
to be case-insensitive[1], while `color-values-from-color-spec' is not:

    (color-values-from-color-spec "rgbi:0/0/0") ;; => (0 0 0)
    (color-values-from-color-spec "rgbI:0/0/0") ;; => nil
    (color-values-from-color-spec "RGBi:0/0/0") ;; => nil
    (color-values-from-color-spec "RGBI:0/0/0") ;; => nil

The closes thing to a specification I could find was [2], that says:

        1.3.2.2.  RGB Intensity String Specification

        An RGB intensity specification in the form of a string is
        identified by the prefix "rgbi:" and whose string conforms
        to the following syntax:

            rgbi:<red>/<green>/<blue>

        Where red, green, and blue are floating point values between
        0.0 and 1.0, inclusive.  The input format for these values
        is an optional sign, a string of numbers possibly containing
        a decimal point, and an optional exponent field containing
        an E or e followed by a possibly signed integer string.

[0] https://man.archlinux.org/man/extra/libx11/XLookupColor.3.en.
[1] https://www.niksula.hut.fi/~jkirma/books/xlib.pdf, section 7.2.2,
    https://www.klauser.ch/lxug/ch14.pdf, page 18.
[2] http://www.nic.funet.fi/pub/X11/X11R4/DOCS/color/Xcms.text

-- 
        Philip Kaludercic