code: function repExplicit(fragment) {
    const inState = new NFAState();
    const outState = new NFAState({
      accepting: true,
    });
  
    // 0 or more.
    inState.addTransition(EPSILON, fragment.in);
    inState.addTransition(EPSILON, outState);
  
    fragment.out.accepting = false;
    fragment.out.addTransition(EPSILON, outState);
    outState.addTransition(EPSILON, fragment.in);
  
    return new NFA(inState, outState);
  }
docs: ----------------------------------------------------------------------------- Kleene-closure 
  Kleene star/closure.
  
  a*