Re: feature request: ability to use occur within *Occur* buffer

[Richard Stallman]

I think the feature you wanted was to be able to selectively keep
just some of the matches already found by the previous M-x occur.
You could sort-of do that by renaming the old *Occur* buffer,
but that would be an inconvenient way to achieve the actual goal.

So I think it is better to modify M-x occur so that, when operating on
an Occur mode buffer, it does "the right thing", filtering the
previous matches but keeping those that remain *as* pointing to the
other buffer that you originally searched.