Listing interfaces in interfaces

Take a look at the following example of an interface definition, this one isfrom the package container/heap:

type Interface interface {
    sort.Interface
    Push(x interface{})
    Pop() interface{}
}

Here another interface is listed inside the definition of heap.Interface, thismay look odd, but is perfectly valid, remember that on the surface an interface is nothingmore than a listing of methods. sort.Interface is also such a listing, so it isperfectly legal to include it in the interface.