Query Builder

Hi Everyone,

 I am trying to fetch JSON response using query builder . My search parameters are something like this

path="/content/......."  & type=cq:Page & p.hits=full & nodename=[A-Z][A-Z][A-Z]

I am interested in fetching page whose name will be a 3 letter word .With the regexp pattern used query I am able to achieve the result but when i use a regexp pattern like [A-Z]{3}  the results are not as expected.

Can someone help me on the restrictions applicable while using regexp in query builder ?

Thanks & Regards,

Krishna