establishes a connection to a X display.
The X display to connect to can be specified ...
- by display, an X display string. If display is an empty string, the DISPLAY environment variable will be used.
- by fd, an open unix file descriptor. auth_string is not relevant here.
cls can be used to customize the connection class. There has to be an X core protocol module loaded, otherwise an XcbException is raised. connect() returns a ready to use instance of cls.