WIPE OUT INVISIBLE CHARACTERS                                      <Alt>+W

  Often when you replace colours or perform certain functions that alter
  colours, you may be left with characters on the screen that are invisible.
  For example if you write some text on the screen and then replace the
  colour of that text with black on black, the text will still be there, but
  you just won't be able to see it.

  This isn't normally a problem, except when you are using the fill command
  - the fill will mistakenly ignore the area with the "invisible" text
  leaving "holes" in the filled area. This function can solve that problem
  by setting any "invisible" characters on the screen to blanks.