some_text [ default_value ] : X
: (which is printed) denotes beginning of the edit buffer (which in this mode is always initially empty). X denotes cursor position. To enter empty using this mode, one has to enter "" (unless redefined by PIL_EMPTY_STRING environment variable).
some_text : default_value X
: (which is printed) denotes beginning of the edit buffer which in this mode is initially set to the default value. X denotes cursor position. To enter empty in this mode one simply has to empty edit buffer using BACKSPACE/DEL keys then press RETURN key.