How to do a full-text search words within some proximity of each other?

I noticed in elastic search (ES), you can do queries like

    "a b"~4

I think this query will match stuff like "a b" and "a x x b" but not
something like "a x x x x x x x x b".

I'm not sure if this kind of thing is possible with postgresql full
text search.   Is it possible?

I understand that I can do a query and rank the results by how closely
the words are to each other, but I want to exclude any matches where
the words are not within two words of each other.

Thanks in advance!

Matt

--
W. Matthew Wilson
matt@tplus1.com
http://tplus1.com