This specification defines an API to provide Web applications with access to various properties of the system which they are running on. Specifically, properties pertaining to the device hardware are addressed. Examples include battery status, current network bandwidth. Additionally, some of those properties offer access to the environment around the device, such as ambient brightness or atmospheric pressure.Remember that's a first working draft which means it's still subject to changes. There's also a nice figure that gives a good overview which APIs one can anticipate in this standard.
Finally, defining APIs are now in vogue within SDOs as W3C is doing it for a while, MPEG has some APIs defined and will continue this path, and I wonder whether IETF is also about to join the API club.