Unlike slots, the parameters are part of the pattern interface. They are filled with values during expansion. From the New Slot Definition dialog, you add new parameters with New Interface Parameter.

In our example of Singleton design pattern, Class Name is a slot that takes alphanumeric Identifier as a parameter. This means that when we pass the word "Foo" as an Identifier parameter to slot named Class Name, we will generate code fragment that has "Foo" as a name of the class.