The Contents of a Class

Separating Metadata and Data

Current Situation Structure descriptions, default attributes, and entity content are described or referenced by the document type declarations within documents. Style sheets are applied by processing instructions.
What belongs in the class? Separating information for a group from information for a document is hard. Entities are often used to create compound documents as one-offs. Still, an important subset of entity usage is declared for multiple documents.
Is a schema metadata? Although the word 'metadata' has received too much use in different contexts, information about information is exactly what schemas are about. Why have we let this sit in the document?