Re: Elisp manual: @section Mode Line Format is unclear (cont.)

[Stephen J. Turnbull]

Sorry about the premature send.  I just got in from playing with my
daughter and my frozen fingers weren't flexible enough to get to C-x C-x....

Prefatory material omitted, here's the beef.

What Alan would like to see, I suppose, is something like:

 - Variable: mode-line-format
     The value of this variable is a mode-line construct which
     describes the mode-line to redisplay.

     The simplest form of mode-line construct is a string containing
     zero or more %-constructs.  A %-construct is a reference to a
     variable whose value is to be interpolated into the modeline at
     that point.  The %-construct is introduced by the character `%',
     followed by optional formatting specifications, and terminated by
     a single character which indicates the variable whose value is to
     be interpolated.  *Note:: %-constructs.  Example:

     `(setq mode-line-format "%B")'

     puts the buffer name, and nothing else, in the mode-line of the
     current buffer.

     A symbol is also a mode-line construct.  Its value is interpolated
     in the mode-line display, but %-constructs are *not* interpreted.
     Example:

     `(setq buffer-format "%B" mode-line-format 'buffer-format)'

     does not have the same effect as the above.  Instead, it produces
     a (rather useless) mode-line containing only the string "%B".

     The mode-line can include images by [however you do that in Emacs].

     Finally, a mode-line construct may be a list of mode-line
     constructs.  If the car is a symbol, the list is treated as a
     conditional.  If the symbol's value is non-nil, the cadr is
     evaluated (recursively, as necessary), and interpolated.
     Otherwise the caddr is evaluated and interpolated.

     If the car is an integer, its magnitude is a target width.  When
     positive, the rest of the elements of the list are evaluated,
     concatenated, and if necessary right-padded with spaces to
     achieve the target width.  When negative, the result is truncated
     to the target width.

     Otherwise, these are evaluated (recursively, as necessary) until
     all resolve to strings, which are concatenated left-to-right to
     produce the mode-line display.  Example:

     `(setq buffer-format "%B" mode-line-format '("%B" buffer-format))'

     displays a mode-line containing the buffer name, followed by the
     string "%B" with no space intervening.

(Note: the above is not likely to be an accurate description of either
XEmacs or Emacs, as there are other, more arcane possibilities.)


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