Sets the copyright for the current page.
At least one field must be set to a non-null value.
Any field not set (or set to
null) will be inherited from the parent(s) in the same book.
Any field set to
"" will have no value and not inherit from parents.
If there are no parent pages in this same book, uses the fields from the book's copyright.
When inheriting a field from multiple parent pages, the field must have exactly the same value in all parents. Any mismatch in value will result in an exception.