Editing Human interface device (section)

=== Physical Descriptor ===
A little known or understood feature of HID is the Physical Descriptor. The Physical Descriptor is used to define the parts of the human body that interact with the individual controls defined in the Report Descriptor.  When controlling a game, the index finger and thumb are usually used to invoke repetitive actions.  Because these fingers are considered to have the fastest 'twitch' response, they are typically used for pulling the trigger of a gun, or activating an often used game function. The Physical Descriptor allows a device vendor identify that which fingers rests on each control and prioritize the set of controls that can be reached by an individual finger. This feature enables a game vendor to intelligently present the best default button mapping, even for a device that didn't exist when the game was developed. The Physical Descriptor also enables full body motion capture information to be presented by a HID device, i.e., the angle, orientation, relative or absolute position of any joint in the human body. And through the Report Descriptor, the motion capture data can be presented at whatever resolution that the device can support.