Mash duplicates any sub-Hashes that you add to it and wraps them in a Mash. This allows for infinite chaining of nested Hashes within a Mash without modifying the object(s) that are passed into the Mash. When you subclass Mash, the subclass wraps any sub-Hashes in its own class. This preserves any extensions that you mixed into the Mash subclass and allows them to work within the sub-Hashes, in addition to the main containing Mash.