How do I find the field in which the match has been found?

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Lucene.NET

Group Members,

I am new at Lucene.Net and using this in my application
In my application I want to know which field of the Document has been matched during search.
So I opted for searcher.explain(). However later I found out that this is a costly approach.
As an alternative I pondered in contrib dlls and saw FastVectorHighlighter class having IsFieldMatch() api. But there is no documentation available stating if this can be used without any performance constraint.
So kindly let me know which is better searcher.explain() or FastVectorHighlighter.IsFieldMatch()

It will also be great if you people suggest me any alternative approach as well.

Regards,
Shubhanshu