code: function() {
      var exp = parsePrimary()
      var t = tokens[0]
  
      if (t === 'X') {
        parser._warn("multiplication in macros should use 'x', not 'X'")
        t = 'x'
      }
      while (t === 'x' || t === '/') {
        tokens.shift()
        var right = parsePrimary()
        exp = {type: t, left: exp, right: right}
        t = tokens[0]
      }
      return exp
    }
docs: parse multiplication and division tokens