[RTCRtpTransceiver-headerExtensionControl.html]
  [the video transceiver.headerExtensionsToOffer() includes mandatory extensions]
    expected: FAIL

  [the audio transceiver.headerExtensionsToOffer() includes mandatory extensions]
    expected: FAIL

  [setOfferedRtpHeaderExtensions throws TypeError on encountering missing URI]
    expected: FAIL

  [setOfferedRtpHeaderExtensions throws NotSupported on encountering unknown URI]
    expected: FAIL

  [setOfferedRtpHeaderExtensions throws InvalidModificationError when setting a mandatory header extension's direction to something else than "sendrecv"]
    expected: FAIL

  [modified direction set by setOfferedRtpHeaderExtensions is visible in headerExtensionsOffered]
    expected: FAIL

  [unstopped extensions turn up in offer]
    expected: FAIL

  [stopped extensions do not turn up in offers]
    expected: FAIL

  [the set of negotiated extensions grows with subsequent offers]
    expected: FAIL

  [the set of negotiated extensions is the set of unstopped extensions]
    expected: FAIL

