By default, any documents saved from Pe get the text/plain MIME type. However, when you save a document from within Pe, take a look at the bottom of the file panel, where you’ll see a drop-down picklist of MIME types to be assigned to the files you save. You can add to the filetypes displayed in this list by including them in the FileTypes section of Pe’s main preferences panel. The new filetypes won’t appear in the picklist until after you’ve closed and restarted Pe.
In addition to the obvious convenience provided here, this feature gives Pe the ability to work around a limitation encountered when you establish a new filetype on your system but don’t have an editor capable of generating that filetype. For example, if you install TrackerBase, you’ll find that it wants to work with files of the type text/trackerbase. But when you create a new file with StyledEdit, it ends up with the type text/plain. One solution to this problem is to simply duplicate existing TrackerBase files, but if you work a lot with Pe, you can simply tell it about the text/trackerbase filetype, and then save them directly into that format.