Hello,

The function "reb-update-overlays" (in lisp/emacs-lisp/re-builder.el)
displays matches in the whole of reb-target-buffer starting at
(point-min) even when the region is active. In keeping with the behavior
of commands like query-replace, replace-regexp and query-replace-regexp,
I modified it so that when the region is active re-builder only displays
matches in the active region. It's behavior is unchanged when the region is
inactive.

I think this change makes sense without disrupting the expectations of
re-builder users.

More generally, I think re-builder needs some work:

1. When the user quits re-builder, the point in reb-target-buffer is not
restored correctly.

2. Without an active region, there should be an option to match forward
or backward from reb-target-buffer's point instead of always matching
from (point-min), with the ability to customize the default behavior.

3. re-builder's overlay system (or some modification of it) can be used
by query-replace-regexp to show matches as the user types.

I am waiting to sign the copyright papers from FSF (which I have
applied for) before sending in these larger patches.

Commit log entry:

* lisp/emacs-lisp/re-builder.el (reb-update-overlays): Restrict
  re-builder matches to region when the region is active.
  
Karthik Chikmagalur