NFA engines compare each element of the regex to the input string, keeping track of positions where they chose between two options in the regex. If an option fails, the engine backtracks to the most recently saved position. For standard quantifiers, the engine chooses the greedy option of matching more text; however, if that option leads to the failure of the match, the engine returns to a saved position and tries a less greedy path. The NFA engine uses ordered alternation, where each option in the alternation is tried sequentially. A longer match may be ignored if an earlier option leads to a successful match.