header-line update

[Oliver Scholz]

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In GNU Emacs 21.1.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2001-10-22 on hermes
configured using `configure  --with-x-toolkit=lucid --with-jpeg --with-xpm 
--with-png --with-tiff'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: de_DE
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

------

According to the Elisp Manual the header-line should be updated
through `force-mode-line-update', too.

This did not work in a package that I am writing, so I evaled the
following in the *scratch* buffer of an Emacs started with `-q
--no-site-file':

(setq header-line-format '(:eval (number-to-string (current-column))))

... then I tried to update the header-line through
`M-: (force-mode-line-update RET)'.

Strangely enough the header-line is updated through vertical movement
of point (`next-line' or `previous-line') but not through horizontal
movement (`forward-char' and `backward-char').

However, it does update constantly -- even without
`force-mode-line-update' if I evaluate `(column-number-mode 1)'.

`current-column' is of course not the only case when
`force-mode-line-update' does not work. It would be a bit complicated
to explain what my package does, though.

    Oliver

------

Recent input:
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <up> <return> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <up> <return> <down> 
<return> F <return> C-x k <return> <up> <down> <up> 
<down> <return> <up> <return> <return> <return> h <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <up> C-SPC <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <up> M-w q q y M-x r e 
p o r SPC e x SPC <backspace> m a SPC b u SPC <ret
urn>

Recent messages:
Saved text from "(setq header-line-format '(:eval (number"

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