make my activity System windows

as the developer android say there are three type on windows how can i use the third one in my activity System windows (ranging from FIRST_SYSTEM_WINDOW to LAST_SYSTEM_WINDOW) are special types of windows for use by the system for specific purposes. They should not normally be used by applications, and a special permission is required to use them. he say must add token but how can i add token to my activity widnow