For example, the text being indexed may be an XML or HTML document and you may only want to index the text content of the elements:
var index = new FullTextIndexBuilder<int>() .WithTextExtraction<XmlTextExtractor>() .Build();
Text extraction is only applied when indexing text, i.e. calls to the
IFullTextIndex.AddAsync overloads. When searching, text extraction is never applied to any query text.