The attached patch adds a defcustom option to allow multiple buffers to
visit the same directory. This became desirable to me for an extension I
wrote (soon to be submitted) to store each chain of dired buffers'
'navigation history' and allow going back/forward to any point in the
history. As you all know, this has been a feature common to all file
*managers* since almost forever; technically dired is a directory
editor, not a file manager, but I expect many will find the feature
desirable, even expected, since all other similar programs have it.

In going through the existing dired code, it seems that some functions
presume that multiple buffers can be visiting the same directory. See:

  dired-find-buffer-nocreate
  dired-fun-in-all-buffers
  dired-clean-up-after-deletion

Also, implicit in the comment for `dired-find-buffer-nocreate' is that
more than one match may exist for a dired directory buffer.

So, maybe this once existed or was planned?

The first patch is for the option. The second patch is a change of
comments to docstrings.

--
hkp://keys.gnupg.net
CA45 09B5 5351 7C11 A9D1  7286 0036 9E45 1595 8BC0