2.1.1444 Part 1 Section 21.2.2.25, catAx (Category Axis Data)

a.   The standard does place any restrictions on the val attribute of the axId element.

Office requires that the val attribute of the axId element matches the val attribute of an axId element in the parent chart.

b.   The standard does place any restrictions on the val attribute of the crossAx element.

Office requires that the val attribute of the crossAx element matches the val attribute of an axId element in the parent chart.