Generic Feature Set
Boolean operators like and/or/not can join words and phrases: e.g. "due process of law" and not ("equal protection" or "civil rights").
Numeric range searching finds any number between two numbers, such as between 3 and 26.
Phonic searching finds words that sound alike, like Smythe in a search for Smith.
Phrase searching finds phrases like: due process of law.
Proximity searching finds a word or phrase within "n" words of another word or phrase: e.g. apple crumble w/25 peach cobbler.
Directed Proximity searching finds a word or phrase "n" words before another word or phrase: apple pie pre/30 peach cobbler.
Stemming finds variations on endings, like applies, applied, applying in a search for apply.
Wildcard support allows ? to hold a single letter place, and * to hold multiple letter places: e.g. appl?sauce and apple*.
Fuzzy Searching finds terms textually similar to one another, e.g. renter, rented.
Thesaurus extension finds terms with similar meanings, e.g. big, large.