Major Description
PostingsHighligher returns for example
[my text with any <b>highlighting</b> followed by more text]
because the PostingsHighligher itself returns for each field a String[] of phrases limited by the beforehand given max phrases. This String[] is the transformed to String using Arrays.toString() at LucenePropertyIndex.java#L688 causing the value to be wrapped in square brackets.
Highlighter returns
my text with any <strong>highlighting</strong> followed by more text
SimpleExcerptProvider returns
<div><span>my text with any <strong>highlighting</strong> followed by more text</span></div>
As the PostingsHighligher cannot get any custom prefix or suffix, I would suggest set <b></b> as default for the others as well to prevent any further text transformation post extracting the excerpts.