One of the principles of Every Page is Page One information design is that an EPPO topic conforms to a type. But I have come to think that that formulation is not quite right. It should really be, an Every Page is Page One topic conforms to a topic pattern.
The difference between type and pattern
What is the difference between a topic type and a topic pattern? In structured writing terms, a topic type, or, more generally, a document type, is a formal set of rules about the structure of a topic which is capable of being expressed by a schema. In most cases, that means an XML schema or something similar. This usage is consistent with the use of the word “type” in other computing applications. A type is a data definition.