SlotRoleHandler represent a declaration of a slot role. They need to have at least the following methods:
* getRoleName()
* getContentModel()
The list of available methods is expected to be expanded to cover behavior of individual slots in different situations, like redirection, countability, and HTML output. The interface is similar in scope to ContentHandler.
To provide access to the available slot roles for a given title, a central SlotRoleRegistry service is needed. It exposes the following methods:
* getSupportedSlotRoles( $title )
* getRequiredSlotRoles( $title )
* getSlotRoleHandler( $title, $role )
The lists returned by getSupportedSlotRoles() and getRequiredSlotRoles() only apply to new edits. There is no guarantee that no revisions exist that violate these constraints.