($m → object{*})
return string
- convert modifiers object as string
function ($m) {
  var convert
  var key
  for (key in $m) {
    if ($m.hasOwnProperty(key) && $m[key] === true) {
      if (isDefine(convert)) convert += '.' + key
      else convert = key
    }
  }
  return convert
}