FLASH MODE                                                            <F4>

  This mode alters the way that the flashing attribute is displayed to make
  the entry of flashing effects easier. There are essentially three states
  that the flashing mode can be in.

  When in normal mode flashing characters are displayed exactly as they
  would be seen. The first time you press <F4> you are transfered to the
  "bright plane" mode. The second time you press <F4> you are transfered to
  the "dark plane" mode. The third time, you will be transfered back to
  normal mode.

  The importance of these two seperate planes, is that if you draw anything
  on them using the ASCII 219 character (#), or the blank character, the
  data for the two planes is kept seperate. When you change back into normal
  mode the two planes are joined together so that the one plane is shown
  during the first phase of flashing, and the second plane is shown during
  the second phase.

  For example, you could write a big "HELLO" on the first plane like this:

                  #   # ##### #     #     #####
                  #   # #     #     #     #   #
                  ##### ###   #     #     #   #
                  #   # #     #     #     #   #
                  #   # ##### ##### ##### #####

  And then swap to the dark plane, and write a big "WORLD" like this:

                  #   # ##### ####  #     ####
                  #   # #   # #   # #     #   #
                  # # # #   # ####  #     #   #
                  ## ## #   # #   # #     #   #
                  #   # ##### #   # ##### ####

  Then, when you swap back into normal mode, the two planes would be
  combined to form a screen that flashed between the words "HELLO" and
  "WORLD".

  There is one limitation on the "dark plane" in that it can only use the
  first 8 "dark" colours (black to light gray). The "bright plane" however
  can use all 16 colours.

  Another advantage of the "bright plane", is that you can change into the
  tiny block mode, and draw more detailed patterns. Note, however, that
  this won't usually work when drawn "on top of" something on the other
  plane.