When connecting IBOUTLETS, what is the significance of having a nothing, a dash?

When conne开发者_运维百科cting outlets in interface builder(by cntrl-clicking) , sometimes I see a "-" proceeding the name of the outlet and sometimes there is nothing there. Of course a dot signifies that there is a connection. But what is the significance of a dash?

From the Xcode user guide:

If a connection identical to the one being made already exists, the menu item is flagged with a dot. If a connection exists with that name, but to a different object, it is flagged with a dash.