docs: function (ch) {
        // DEBUG "Processing `" + ch + "`:"
        var nextStates = this.nextStates,
            child,
            charSpec,
            chars;
  
        // DEBUG "  " + debugState(this)
        var returned = [];
  
        for (var i = 0, l = nextStates.length; i < l; i++) {
          child = nextStates[i];
  
          charSpec = child.charSpec;
  
          if (typeof (chars = charSpec.validChars) !== 'undefined') {
            if (chars.indexOf(ch) !== -1) {
              returned.push(child);
            }
          } else if (typeof (chars = charSpec.invalidChars) !== 'undefined') {
            if (chars.indexOf(ch) === -1) {
              returned.push(child);
            }
          }
        }
  
        return returned;
      }