Many PC programs have an "undo" feature which comes in handy when you do something you really didn't want to do.
I've developed a method to simulate undo for SEU which I think you'll find useful. The procedure works because when you edit a source member, the member residing on disk is not changed until later. SEU makes a copy of it for you to work with. As you exit (F3) from edit mode and save your work, SEU overlays the original member on disk with the one you just finished editing.
When you realize that you have inadvertently deleted a line or modified it beyond recognition, do the following:
1. Press F15 to access the Browse/ Copy Options screen. Unless you have used this screen previously in the current editing session, the default options should be filled in. The Selection field should contain a 1 and the Browse/copy member, File and Library fields should be the same as the member you are editing.
2. Press Enter. The source member you are editing appears on the bottom of the screen, but it doesn't reflect any of the changes that you made in the current editing session. You may need to page down to see the lines you want restored.
3. Use the C or CC line commands to copy the lines that you want to restore. You can then copy them to the top half of the screen to modify the member you are editing.
4. Press F12 to remove the split screen.
Alternatively, you could just exit (F3) out of the session and specify an "N" in the Save member field. In this case, you will lose all changes you have made to the member.