Constant regex_automata::dfa::DEAD

const DEAD: StateID;

This is an alias for a state ID of zero. It has special significance because it always corresponds to the first state in a DFA, and the first state in a DFA is always “dead.” That is, the dead state always has all of its transitions set to itself. Moreover, the dead state is used as a sentinel for various things. e.g., In search, reaching a dead state means that the search must stop.