Over on GitHub, two Googlers – Reilly Grant and Ken Rockot – have published an unofficial draft describing the WebUSB API for direct access to USB devices from web pages. It’s considered a public working draft of a potential specification as it has no official standing whatsoever and doesn’t represent broader support of any standards.
The draft gets into security and privacy considerations as well as descriptors and requests, and device enumeration and usage (transfers, configurations, interfaces, and endpoints).
You can browse the whole 6-part document here. It will be interesting to see how the project progresses and if it picks up significant support.