The editor has two text-input modes:

Insert and overstrike modes are common to all editors: if one editor is in insert mode, all editors are in insert mode. To configure the cursor appearance, choose Tools > Options.

To toggle between insertion and overstrike mode:

When overstrike mode is enabled, the mode indicator changes from INS to OVR and the cursor will change to the overstrike cursor.

To add or insert text:
  1. Move the insertion point to the place text is to be inserted.
  2. Enter the text using the keyboard.

To overwrite characters in an existing line, press the Insert key to place the editor into overstrike mode.