function bitwiseassignop(s) {
    symbol(s, 20).exps = true;
    return infix(s, function(context, left, that) {
      if (state.option.bitwise) {
        warning("W016", that, that.id);
      }

      checkLeftSideAssign(context, left, that);

      that.right = expression(context, 10);

      return that;
    }, 20);
  }
Convenience function for defining JSHint symbols for bitwise assignment
operators. See the `assignop` function for more detail.

@param {string} s - the name of the symbol

@returns {object} - the object describing the JSHint symbol (provided to
                    support cases where further refinement is necessary)