[gosub]

Well, a patch is defined as Patch [Edit a], so I presume the sequence of the edit is implicit in the list position. The article says that an edit is the modification of an element of a Vector. I think the parameter a is the type of the elements of the Vector. In your example, a Patch File would be something to apply to a Vector File, and the Int in the edit should be the index of the file in the vector.