The subschemaFinal method option indicates that the method can be extended or reimplemented in its local schema but not in a subschema.
Use the subschemaFinal option to make methods available to other schemas but prevent those schemas from modifying, reimplementing, or circumventing the defined method behavior. As an example, consider the following situation.
Schema A
Class C1 - method m1 : subschemaFinal
Class C2 - subclass of C1
Class C3 - subclass of C2
As the developer of schema A, you may want to specify that method m1 cannot be reimplemented in a subschema. Making method m1 in class C1 subschemaFinal accomplishes this.