UnifiedHighlighter doesn't highlight MTQ wrapped in BoostQuery.
For example, suppose we have a doc with a field 'f' contains data 'lucene'.
UnifiedHighlighter highlights query (f:lucene*), but query (f:lucene*)^1 doesn't. Test code:
My opinion it's because MultiTermHighlighting.extractAutomata() returns an empty automaton for BoostQuery. I think, should add some thing like: