W3C Web Content Accessibility Guidelines (WCAG) 2.0 ...

If the request packet specifies WDSMCSE_OPT_IPV6_CAPABLE, and it is set to 1, and the server is capable of setting up multicast session for IPv6, then the server MUST set up the multicast session using IPv6; otherwise the server MUST set up the multicast session using IPv4. ................
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