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(elisp)Edebug Display Update

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Edebug Display Update
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   When Edebug needs to display something (e.g., in trace mode), it
saves the current window configuration from "outside" Edebug (Note:
Window Configurations).  When you exit Edebug (by continuing the
program), it restores the previous window configuration.

   Emacs redisplays only when it pauses.  Usually, when you continue
execution, the program re-enters Edebug at a breakpoint or after
stepping, without pausing or reading input in between.  In such cases,
Emacs never gets a chance to redisplay the "outside" configuration.
Consequently, what you see is the same window configuration as the last
time Edebug was active, with no interruption.

   Entry to Edebug for displaying something also saves and restores the
following data (though some of them are deliberately not restored if an
error or quit signal occurs).

   * Which buffer is current, and the positions of point and the mark
     in the current buffer, are saved and restored.

   * The outside window configuration is saved and restored if
     `edebug-save-windows' is non-`nil' (Note: Edebug Display Update).

     The window configuration is not restored on error or quit, but the
     outside selected window _is_ reselected even on error or quit in
     case a `save-excursion' is active.  If the value of
     `edebug-save-windows' is a list, only the listed windows are saved
     and restored.

     The window start and horizontal scrolling of the source code
     buffer are not restored, however, so that the display remains
     coherent within Edebug.

   * The value of point in each displayed buffer is saved and restored
     if `edebug-save-displayed-buffer-points' is non-`nil'.

   * The variables `overlay-arrow-position' and `overlay-arrow-string'
     are saved and restored.  So you can safely invoke Edebug from the
     recursive edit elsewhere in the same buffer.

   * `cursor-in-echo-area' is locally bound to `nil' so that the cursor
     shows up in the window.