in c#, best slight format twine xml?

i am formulating lightweight editor c# know best slight converting twine simply formatted xml string. i wish there's open slight c# library "public bool formatasxml(string text, out twine formattedxmltext)", nonetheless couldn't easy, it?

very specifically, slight "somemethod" have furnish cost below?

string unformattedxml;
string formattedxml;

unformattedxml = "<?xml version=\"1.0\"?><book><author>lewis, c.s.</author><title>the 4 loves</title></book>"
formattedxml = somemethod(unformattedxml);

console.writeline(formattedxml);

output:

<?xml version="1.0"?>
  <book id="123">
    <author>lewis, c.s.</author>
    <title>the 4 loves</title>
  </book>