A product with closed functions remains bound by the rest of the standard, clause 5.1 standing in for any clause that excludes closed functionality. Its closed functions have to be usable with no assistive technology supplied, attached or installed by the user, and must meet whichever parts of 5.1.3 through 5.1.6 are relevant; a user's own headset or induction loop does not count as assistive technology for this test.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.