sorry for not answering before but Google decided to hide forum notifications from me.
If you want to insert xml as a content or content which is inside of xml you will have to do it manually. There is no automatic way how to do it. If the idea is to insert XML code then code has to be pasted and selected as preformatted text.
It is different in the new editor where editor can handle different kind of blocks but that version is not going to be out for couple of months.