Payloads for multiValued fields?

[Alf Eaton]

When searching a multiValued field, is it possible to know which of  
the multiple fields the match was in?

For example if I have an index of documents, each of which has  
multiple image captions stored in separate fields, I'd like to be  
able to link from the search results to the caption in the original  
document.

One possibility could be attaching metadata to a field, similar to  
payloads for terms. At the moment all I can think of is adding  
metadata inside the stored field and stripping that out when it's  
indexed and displayed, but that's not ideal.

alf.