Javadoc
Sets the element identifier to apply the action.
If the type is "jid", then the 'value' attribute MUST contain a valid Jabber ID.
If the type is "group", then the 'value' attribute SHOULD contain the name of a group
in the user's roster.
If the type is "subscription", then the 'value' attribute MUST be one of "both", "to",
"from", or "none".