|SOURCE|
[Common::System::Window]
* GetCurrentScreenNumber returns a signed integer instead of an unsigned
  integer, which allows for non-valid screens to be returned (non-positive)
[Linux::System::LinuxWindow]
* GetCurrentScreenNumber queries the DISPLAY environment variable, working
  backward from the end of the DISPLAY string until the period character is
  encountered, the string resulting from this is converted into a signed
  integer and returned
* GetCurrentScreenNumber returns -1 if the DISPLAY environment variable is not
  valid