Could you please run my code on your machine to verify that it works on
your machine but not mine.

On Wed, 29 Dec 2021 at 06:51, Eli Zaretskii <eliz@gnu.org> wrote:

> [Please keep the list address on the CC.]
>
> > From: Davin Pearson <davin.pearson@gmail.com>
> > Date: Tue, 28 Dec 2021 16:58:50 +1300
> >
> > In your email to me you said that one of the foreground colours
> > will "win" and the other will be ignored.  What I want is the
> > same thing for the background colour.  As far as I understand the
> > winning foreground colour will be the one that is added last in
> > the fontification spec, and with the symbol 'end added to
> > font-lock-add-keywords.
> >
> > Here is my font-lock-string-face
> >
> > "assdsdasd"
> >
> > Here is the text dmp-asdssd coloured in my choice of colours: red
> > and green:
> >
> > "dmp-asdssd" (*)
> >
> > Here is the code that fontifies the above code.
> >
> > (make-face 'dmp-face--line0--col1-red)
> > (set-face-foreground 'dmp-face--line0--col1-red "#ff0000")
> > (set-face-background 'dmp-face--line0--col1-red nil)
> > (make-face-bold 'dmp-face--line0--col1-red)
> >
> > (make-face 'dmp-face--line0--col2-green)
> > (set-face-foreground 'dmp-face--line0--col2-green "#00ff00")
> > (set-face-background 'dmp-face--line0--col2-green nil)
> > (make-face-bold 'dmp-face--line0--col2-green)
> >
> > (make-face 'dmp-face--line0--col3-blue)
> > (set-face-foreground 'dmp-face--line0--col3-blue "#0000ff")
> > (set-face-background 'dmp-face--line0--col3-blue nil)
> > (make-face-bold 'dmp-face--line0--col3-blue)
> >
> > Here are some useful constant strings:
> >
> > (defvar dmp-defun-inner-regexp-less-dash+star
> "a-zA-Z0-9_.!@$%^&=<>/|+:;?~")
> > (defvar dmp-defun-inner-regexp-less-dash      (concat ""
> dmp-defun-inner-regexp-less-dash+star))
> > (defvar dmp-defun-inner-regexp-less-star      (concat "-"
> dmp-defun-inner-regexp-less-dash+star))
> > (defvar dmp-defun-inner-regexp                (concat "-,"
> dmp-defun-inner-regexp-less-dash+star))
> > (defvar dmp-defun-outer-regexp                (concat "["
> dmp-defun-inner-regexp            "]+"))
> > (defvar dmp-bra                               "\\(^\\|[][
> \t\r\n()'\",.:=]\\)")
> > (defvar dmp-ket                               "\\($\\|[][
> \t\r\n()\",.:=]\\)")
> >
> > Here is the actual font lock code:
> >
> > (defun dmp-getting--syntax-highlighting--online ()
> >   (font-lock-add-keywords
> >    'emacs-lisp-mode
> >    '(
> >      (, (format "\\(dmp[0-9]\\)\\(\\(-[%s]+\\)+\\)%s"
> >                 dmp-defun-inner-regexp-less-dash
> >                 dmp-ket)
> >         (1 'dmp-face--line0--col1-red t)
> >         (2 'dmp-face--line0--col2-green t)
> >         )
> >      (, (format
> "\\(dmp[0-9]\\(-[%s]+\\)\\)\\(\\([-_][-_]\\|:\\)[%s]+\\)%s"
> >                 dmp-defun-inner-regexp-less-dash
> >                 dmp-defun-inner-regexp
> >                 dmp-ket)
> >         (1 'dmp-face--line0--col1-red t)
> >         (3 'dmp-face--line0--col2-green t))
> >      (, (format
> "\\(dmp[0-9]*\\(-[%s]+\\)*\\)\\([_-][_-][%s]+\\)\\([_-][_-][%s]+\\)%s"
> >                 *dmp-defun-inner-regexp-less-dash*
> >                 *dmp-defun-inner-regexp*
> >                 *dmp-defun-inner-regexp*
> >                 *dmp-ket*)
> >         (1 'dmp-face--line0--col1-red t)
> >         (3 'dmp-face--line0--col2-green t)
> >         (4 'dmp-face--line0--col3-blue t))
> >      )
> >    'end)
> >   )
> > (add-hook 'font-lock-mode-hook 'dmp-getting--syntax-highlighting--online
> 'APPEND)
> >
> > Notice that in the text marked with a (*) the background colour
> > of the above text is the same as the background colour of the
> > screen.
> >
> > When dmp-face--line0--col1-red, dmp-face--line0--col2-green and
> > dmp-face--line0--col3-blue 's set-face-foreground set to nil, as it
> > is above, I want the for the string face's background colour to
> > show through as light blue in the fontification of dmp-asdssd.
>
> I think this is something that your code does.  If I just merge two
> faces, one with a background color, the other with a foreground color,
> the result of the merge has the background of the first faces and the
> foreground of the second.
>
> So I conclude that something goes wrong in your
> dmp-getting--syntax-highlighting--on-line function, or in how it
> interacts with font-lock.
>