MuEdit is stationery-aware. The File Save dialog contains a checkbox "As Stationery" which you can use to save stationery documents. When you try to open a document which is a stationery, then MuEdit will instead open a copy of that document in an "Untitled" window.
MuEdit does not allow editing the same document in more than one window. (Documents with the same name in different folders are treated as different documents.) When a file is being edited in one window, and you try to save another window in the same file, you will get the message "This file is already open."
