Re: undo-information kept for *occur*

[Richard Stallman]

    > I use "occur" on big (> 100 MB) text-files quite often. While doing the 
    > very nice filtering, emacs regularly, but not always, output a message 
    > about the undo-information that prompts me to give it a yes or no 
    > aswear. I cannot exactly remember the wording, but yes means "yes, go 
    > along and drop the ability to undo the changes in the *occur* buffer".
    > 
    > Could this kind of behaviour be avoided? I can see no occasion when I 
    > would like to undo in an *occur*-buffer.

Emacs turns off undo data generation while computing the *occur* buffer:

    (defun occur-engine (regexp buffers out-buf nlines case-fold-search
                                title-face prefix-face match-face keep-props)
      (with-current-buffer out-buf
        (let ((globalcount 0)
              ;; Don't generate undo entries for creation of the initial 
contents.
              (buffer-undo-list t)
              (coding nil))
              ...

So why does it build up a lot of undo records?