What is line editor?
Way back in the early days of Natural, there was only one editor, the line editor.
As it’s name implies, you could only work on one line at a time. Shortly after the first release of Natural the current mainframe editor was released.
The current editor, which is probably what you are using if you are on the mainframe, is far more functional than the original line editor. You can copy/delete/insert groups of statements; you can insert code from other programs; the list goes on and on.
The line editor is still available. It is documented under System Commands. It is invoked with the EDT command. Typically it is used in batch mode.