Calibre's comment editor will always convert your text to HTML format. It is not possible to save a Markdown format through the GUI.
The "Markdown only from plain text" function is there only for some very rare cases when the text is incorrectly saved inside the
metadata.db database file (hence the existence "always convert" for the others case).
For your suggestion to convert the double-dashes (--) into a proper em-dash (—), I am obliged to refuse :
The philosophy of
Comments Cleaner is to never modify the text, only the CSS formatting.
For all text editing, I advise you to use the "Search and Replace" option in the mass meta-data editor. It is possible to save an operation.
Nevertheless, you are the second person to make me a similar suggestion (edit the text), and that gives me an idea:
Make a similar plugin that will run a list of "Search and Replace" operations (based on the saved config in the mass meta-data editor)
