Type , then move the cursor so the starting and ending cursor positions form the opposite corners of a rectangle. Then type . The area inside the rectangle will be filled up with spaces. Saves the current file and gets another one. See the command.
Deleted stuff is recoverable by typing .
The stuff can be put anywhere, as many times as desired. The buffers can be as often as desired. In a parameter, erases the latest character typed. Moves the cursor to the next tab stop. Has no effect on the file.