This is in the help for both V16 and V17:
I suspect that should say something like
There's a similar situation in the help for the command WINDOW.
ACTIVATE ... type One or more of the following values: ... 4 - flash continuously until WINDOW is called again with the /FLASH type set to 0 ...
4 - flash continuously until either ACTIVATE or WINDOW is called again for this window with the /FLASH type set to 0