My only other question is whether this notation could be extended (if it doesn't allow it already) to include not just a schema but the data inside it. My guess is it would then look a bit like a data structure serialized into perl..

It's for specifying the schema, such as with DTD or LDAP schema. If you're looking for transfering data, you probably want to look at YAML, JSON, WDDX or some other interchange format.