Last update: Mon, Feb 13, 2017 at 7:32 PM.

Right now there is no user interface in the OPML Editor for setting this attribute, but you can do it from the Quick Script window.

1. Place the cursor top line of the document.
2. Press Cmd-; to open the Quick Script window.
3. Enter: op.attributes.setone ("allLevels", true) and press Enter.
4. Click the Save button.