The Selectors Pane shows the list of message selectors that are present in the currently selected protocol. Selecting one of these selectors will display the classes that implement this protocol in the Conforming Classes Pane of the browser.
The context menu for this pane allows you to add and remove selectors from the protocol. If you choose to add a new selector to a protocol then all conforming classes that do not yet implement or inherit this message will have a stub method created for them.
Note that you cannot add or remove selectors from a protocol that is locked.