X(A|B||C|D)Y XXXYYY y $& XY # Trie w/ NOTHING
(?i:X([A]|[B]|y[Y]y|[D]|)Y) XXXYYYB y $& XY # Trie w/ NOTHING
^([a]{1})*$ aa y $1 a
+a(?!b(?!c))(..) abababc y $1 bc # test nested negatives
+a(?!b(?=a))(..) abababc y $1 bc # test nested lookaheads
+a(?!b(?!c(?!d(?!e))))...(.) abxabcdxabcde y $1 e
+X(?!b+(?!(c+)*(?!(c+)*d))).*X aXbbbbbbbcccccccccccccaaaX y - -