BQS — specifications of multiplicity and other semantics in UML diagram normative

This AB member asked the author during the AB meeting whether the UML
diagram is intended to be normative. For example, multiplicities on
references are 0..1 in some cases and 1 in other cases, indicating in the
former cases that a null value is acceptable and in the latter cases that a
null value is not acceptable. The question is whether the author intended
such specifications of multiplicity and other semantics in the UML diagram
to be normative. The author answered that they are intended to be
normative. However, the document calls the diagram "illustrative."

see below