USB Device BOS descriptor structure.
The BOS descriptor (Binary device Object Store) defines a root descriptor that is similar to the configuration descriptor, and is the base descriptor for accessing a family of related descriptors. A host can read a BOS descriptor and learn from the wTotalLength field the entire size of the device-level descriptor set, or it can read in the entire BOS descriptor set of device capabilities. The host accesses this descriptor using the GetDescriptor() request. The descriptor type in the GetDescriptor() request is set to BOS.