How does MultiSearcher Work

[wu fox]

Hi :
  I'd like to search several indices located at diffrence partition.I think
use MultiSearcher is the right way.But when I inspected the source code of
this class,I was confused because  I can not find any code that seach all
the indices and combine the result ,how does this class do this job?Any help
will be appreciated
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爱生活，爱FOX