Here are the data structures with brief descriptions:

Cei	The main context to interact with libei
Cei_device	A single device to generate input events from
Cei_event	An event received from the EIS implementation
Cei_keymap	An keymap for a device with the EI_DEVICE_CAP_KEYBOARD capability
Cei_region	A rectangular region, defined by an x/y offset and a width and a height
Cei_seat	A logical seat for a group of devices
Ceis
Ceis_client
Ceis_device
Ceis_event
Ceis_keymap
Ceis_region	Regions are only available on devices of type EIS_DEVICE_TYPE_VIRTUAL
Ceis_seat
Ceis_touch
Coeffis	The main context to interact with liboeffis