2.1.1437 Part 1 Section 220.127.116.11, crossAx (Crossing Axis ID)
a. The standard states that the values of the val attribute are defined by the XML Schema unsignedInt datatype.
Office restricts the value of this attribute to be at most 2147483647.
b. The standard does not 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.