INSERT MODE    (default)

  Sets the mode of the current buffer to insert, as opposed to overstrike.
  As you type, the new text is inserted at the current position, pushing
  existing text to the right and down.

  Usage notes:

  o  The mode of the buffer is shown in the status line. It also affects
     some commands and keys such as DELETE, ERASE CHARACTER, and RESTORE
     CHARACTER.

  o  If you use SET BOX NOPAD, the mode of the buffer affects box editing.
     In insert mode, cutting a box makes text to the right of the box
     "collapse" to the left, closing the gap, and pasting a box pushes
     existing text to the right. To override these effects without changing
     your settings, use BOX CUT OVERSTRIKE and BOX PASTE OVERSTRIKE.

  o  If your system has a mouse, you can toggle the mode of the buffer by
     clicking M1 on the Insert or Overstrike indicator in the status line.
     This works on DECwindows, DECterm, or UIS. See help on Status Line.

  Related topics:

     Status Line     CHANGE MODE     OVERSTRIKE MODE     SET BOX NOPAD