Each private format must have a unique identification number. To obtain an identification number, the application registers the name of the private format in the system atom table. The system assigns a unique identification number for the format name. Other applications having access to the format name can query the system atom table for the format identification number.

An application can interpret its own private formats and request them from the clipboard for cutting and pasting its own data. Other applications that know the private-format identification number also can interpret the formatted data.