WRITEWIN expression [ , expression [ , expression ... ] ]

   Synopsis:
      Writes text to the task window

   Notes:
      The first expression is the text to write.
      The remaining optional expressions specify how the text should be
         displayed. The expressions can be any of the following strings, in any
         order:
         
         "empty"     - Empties the window, before writing the text
         "echo"      - Writes the text on the end of the last line
         "nl"        - Writes the text on a new line (default)
         "black", "red", "green", "yellow", "blue", "magenta", "cyan", "white"
                     - Sets the text colour
         "ul_black", "ul_red", "ul_green", "ul_yellow", "ul_blue", "ul_magenta",
            "ul_cyan", "ul_white"
                     - Sets the underlay (foreground) colour
         "italics"   - Writes the text in italics
         "underline" - Writes the text underlined
         "blink_slow"
                     - Writes slowly-blinking text
         "blink_fast"
                     - Writes quickly-blinking text
         "strike"    - Writes the text with a strike-through line

      Any of the colour expressions can be specified IN CAPITALS to make them
         bolder (e.g. "RED", "GREEN", "UL_BLUE").
      Only the first text colour and the first underlay colour are used. 
         Multiple text/underlay colours are ignored.
      If the task window has been 'painted' with a PAINTWIN statement, using the
         WRITEWIN statement with any colour strings causes the window to revert
         to its default black-and-white colour scheme.

      If the task window is not open, WRITEWIN statements are ignored (and no
         error message is generated). However, if OPTION DIVERT has been
         specified, the text is diverted to the 'main' window.

   Examples:
      ! No special effects
      WRITEWIN "Hello world!"
      
      ! Green text
      WRITEWIN "Hello world!", "green"
      
      ! Green text on a yellow underlay
      WRITEWIN "Hello world!", "green", "ul_yellow"
      
      ! Green text on a yellow underlay, in italics and underlined
      WRITEWIN "Hello world!", "underline", "italics, "ul_yellow", "green"
      
      ! Empty the window first
      WRITEWIN "Hello world!", "empty"
