Fixing typo ("cannot" repeated twice) (JC Brand).
If the sender knows only the recipient's bare JID, it cannot cannot determine (via &xep0030; or &xep0115;) whether the intended recipient supports the Chat Markers protocol. In this case, the sender MAY send a Chat Marker or markable message.
+If the sender knows only the recipient's bare JID, it cannot determine (via &xep0030; or &xep0115;) whether the intended recipient supports the Chat Markers protocol. In this case, the sender MAY send a Chat Marker or markable message.
If the sender knows a full JID for the recipient (e.g., via presence), it SHOULD attempt to determine (via service disco or entity capabilities) whether the client at that full JID supports the Chat Markers protocol before attempting to send a Chat Marker or markable message.