intangibility in buffer-menu

[Luc Teirlinck]

Customize `Buffer-menu-use-header-line' to off (nil).

Do: M-x buffer-menu

With point at the beginning of the buffer, C-n stays stuck.  This bug
looks a lot like the one reported by Klaus, but the problem starts at
a different place, later in `line-move-finish'.  The bug is related to
intangibility and appears to occur when an intangible region covers
two or more newlines.  Stefan has suggested to change some aspects of
the treatment of intangibility, although he has not yet specified
which ones.  Maybe these changes might take care of this bug
automatically or this bug might be relevant to that discussion.

The intangible region of the buffer menu is:

CRM Buffer                Size  Mode              File
--- ------                ----  ----              ----

Maybe unrelated point, but since we are looking at
`Buffer-menu-use-header-line' anyway and since it also might be
relevant to any discussion about intangibility:

Why is this region made intangible?  This seems to completely
contradict the philosophy behind `Buffer-menu-use-header-line'.

Normally this information is in a header line.  The user customizes
this variable because he wants that information as a regular
"no-tricks" part of the buffer, so he can move into it, cut and paste,
whatever.  Instead, he gets confronted with all kinds of odd behavior,
which might look extremely strange and confusing if he is not familiar
with the intangibility property, and, in fact, maybe even if he is.

If intangibility is removed, the user will only move inside the now
intangible region if he chooses to do so.  No horrible calamities are
going to happen if he does.  Whether it is actually useful or not is
up to the user to decide.

The absolute only advantage I can see to intangibility is that if the
bug got fixed, the user could move out of the region with one instead
of two C-n's.  That does not seem worth confusing the user with all
kind of strange behavior.  If the user did not want to have anything
to do with that region, he would be happy with the default value of
`Buffer-menu-use-header-line' and have the stuff in a header.

Sincerely,

Luc.