[Zope-CMF] Why can't I search for a document that contains a number rather than a word?

[suresh_vv]

I am doing a search for a number (like 21) which is present in the 
Description field of a document. It is not returned in the search. If 
I search for any words (alphabetic) then the document is found in the 
search.

I am using CMF 1.3

Any help appreciated.

Suresh