Table of Contents

Highlighting

Highlighter extracts a snippet from stored text and wraps matching terms in tags.

Use it

using Rowles.LeanLucene.Search;

var hl = new Highlighter(preTag: "<mark>", postTag: "</mark>", analyser: new StandardAnalyser());

Query q = new TermQuery("body", "fox");
var terms = Highlighter.ExtractTerms(q);

string snippet = hl.GetBestFragment(
    text: storedBody,
    queryTerms: terms,
    maxSnippetLength: 200);

Term extraction

Highlighter.ExtractTerms(Query) returns a HashSet<string> of lowercased terms the query would match. It walks the query tree, including boolean and phrase clauses.

Tags and analyser

The default tags are <b> and </b>. The analyser should match the one used at index time, or token boundaries will not align.

What "best fragment" means

The snippet is the highest-scoring window in the source text by query-term density, truncated to maxSnippetLength characters with ellipsis when needed. Returns the truncated original when no terms match.

See also

  • <xref:Rowles.LeanLucene.Search.Highlighter>
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