Like {@link StopFilter} except it will not remove thelast token if that token was not followed by some token separator. For example, a query 'find the' would preserve the 'the' since it was not followed by a space or punctuation or something, and mark it KEYWORD so future stemmers won't touch it either while a query like "find the popsicle' would remove 'the' as a stopword.
Normally you'd use the ordinary {@link StopFilter}in your indexAnalyzer and then this class in your queryAnalyzer, when using one of the analyzing suggesters.