How to know the matched field?

[Paul Libbrecht]

Hello list,

in an auto-completion task, I would like to show to the user the field  
that's been matched against the query in the found document.

Typically, my documents have multiple fields for each field-name and I  
would like the index's findings to give me the field used. How can I  
do that?

It seems to me a task of the highlighter (or of the QueryScorer?) but  
I am actually not interested into extracting the fragment found just  
to know the exact field found.

thanks in advance

paul