The discussion on p. 46 might lead to confusion about namespaces and schemas. It says:
For such a document with no namespace, your XML editor might be unable to check your document for vocabulary-specific validity; it would only be able to check for well-formedness.
A document without namespaces may or may not have a schema, just like a document with namespaces. If it has a schema association, with or without namespaces, it can be checked for vocabulary-specific validity.
The discussion on p. 46 might lead to confusion about namespaces and schemas. It says:
A document without namespaces may or may not have a schema, just like a document with namespaces. If it has a schema association, with or without namespaces, it can be checked for vocabulary-specific validity.