Implement default help-echo for mode line.

* lisp/bindings.el: Remove explicit help-echo from format-mode-line.
(mode-line-front-space, mode-line-end-spaces)
(mode-line-misc-info): New variables.
(mode-line-modes, mode-line-position): Move the default value to
the variable definition.
(mode-line-default-help-echo): New defcustom.

* src/buffer.c (buffer_local_value_1): New function, split from
Fbuffer_local_value; can return Qunbound.
(Fbuffer_local_value): Use it.
(Vmode_line_format): Docstring tweaks.

* src/xdisp.c (calc_pixel_width_or_height): Use Fbuffer_local_value.
(note_mode_line_or_margin_highlight): If there is no help echo,
use mode-line-default-help-echo.  Handle the case where the mouse
position is past the end of the mode line string.

* doc/lispref/modes.texi (Mode Line Data): Use "mode line construct"
terminology for consistency.

2 files changed, 7 insertions, 2 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 850b3f9cf54..b774809feb9 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2012-06-03  Chong Yidong  <cyd@gnu.org>
+
+        * modes.texi (Mode Line Data): Use "mode line construct"
+        terminology for consistency.
+
 2012-05-27  Glenn Morris  <rgm@gnu.org>
 
         * abbrevs.texi, advice.texi, anti.texi, backups.texi:
diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index 8dca250ce10..96e9b78f871 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -1843,9 +1843,9 @@ properties specified by @var{props} to the result.  The argument
 A list whose first element is a symbol that is not a keyword specifies
 a conditional.  Its meaning depends on the value of @var{symbol}.  If
 @var{symbol} has a non-@code{nil} value, the second element,
-@var{then}, is processed recursively as a mode line element.
+@var{then}, is processed recursively as a mode line construct.
 Otherwise, the third element, @var{else}, is processed recursively.
-You may omit @var{else}; then the mode line element displays nothing
+You may omit @var{else}; then the mode line construct displays nothing
 if the value of @var{symbol} is @code{nil} or void.
 
 @item (@var{width} @var{rest}@dots{})