code: function() {
          gobbleSpaces();
          var to_check = expr.substr(index, max_binop_len),
            tc_len = to_check.length;
          while (tc_len > 0) {
            if (binary_ops.hasOwnProperty(to_check)) {
              index += tc_len;
              return to_check;
            }
            to_check = to_check.substr(0, --tc_len);
          }
          return false;
        }
docs: `index` stores the character number we are currently at while `length` is a constant All of the gobbles below will modify `index` as we move along