[bdbxml] A question about indices in Berkeley XML DB

Hi,
 I have a question with regard to the using of indices in Berkeley XML DB.
 Are the indices used to index the documents in a container?
 If yes, can they be used to index a single document in a container (e.g. 
index an element or attribute value)?
 For example, I put a large xml document to a container and try to query 
some nodes with this document.
 How should I use indices for this scenario?
  Thanks
 Leon