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https://issues.apache.org/jira/browse/LUCENE-1302?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12603929#action_12603929
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Hoss Man commented on LUCENE-1302:
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FWIW: Paul's comment is exactly what i was trying to get at.
The only reason Explaination.isMatch returns true for positive scores without
requiring that the match state be specified explicitly was is so it would be
backwards compatible for older legacy query types (possibly created by lucene
users) when the match/score semantics where clarified in order to allow/support
negative scores for matching documents.
> explain should not mask negative scores
> ---------------------------------------
>
> Key: LUCENE-1302
> URL: https://issues.apache.org/jira/browse/LUCENE-1302
> Project: Lucene - Java
> Issue Type: Bug
> Components: Query/Scoring
> Reporter: Doron Cohen
> Assignee: Doron Cohen
> Priority: Minor
> Fix For: 2.4
>
> Attachments: lucene-1302-explain-negative.patch
>
>
> Explanation.isMatch() returns false for 0 or negative scores.
> Hence negative scores are omitted from the explanation.
> This causes, when using e.g. BoostingTermQuery with negative boosts, a
> difference between the collected doc score and the score shown by explain().
> A word on the usage of this - BTQ with negative boosts is useful for
> "punishing" documents for containing a term. It also allows all sorts of
> tricks with multiplying query boost by the BTQ boost, so you get a positive
> score if both boosts have the same sign but negative otherwise. - I am sure
> there other uses as well.
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