This header is used for specifying features of the protocol that are supported. Different features may apply to different entries in a server-side playlist.

The Supported header is defined only for servers with a version greater than or equal to 9.0 (as specified by the server in the Server header) and only for clients with a version greater than or equal to 9.0 (as specified by the client in the User-Agent header).<44>

The syntax of the Supported header is defined as follows:

 WMCfeat   = "com.microsoft.wm.fastcache"

             / "com.microsoft.wm.predstrm"

             / "com.microsoft.wm.srvppair"

             / "com.microsoft.wm.sswitch"

             / "com.microsoft.wm.startupprofile"

 Supported = "Supported: " WMCfeat *4["," [SP] WMCfeat]

             CRLF