The open specification doesn't really even mean much, because the specification covers how the DRM module interfaces with the browser, not compatibility between

The open specification doesn't really even mean much, because the specification covers how the DRM module interfaces with the browser, not compatibility between DRM modules. In practice, there is exactly one DRM implementation used on the web, and it is proprietary (Wildvine). You could implement another standard-compliant DRM scheme, but no one would use it; the value of the standard is basically nil.