This is called for any characters that don't have a registered handler. Whatever the encoding in the original document, the string is returned to the handler in UTF-8. This is called for a declaration of an unparsed entity. Entity is the name of the entity. Pubid is the public id.
Notation is the notation name.
Base and Pubid may be undefined. This is called for a declaration of notation. Notation is the notation name. Pubid is the public id. Base, Sysid, and Pubid may all be undefined.