2.1.1512 Part 1 Section 18.104.22.168, pt (String Point)
a. The standard states that the values of the idx 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 state uniqueness or maximum value restrictions for the idx attribute.
Office requires that the idx attribute be unique amongst siblings and be between 0 and the total points in the parent element minus one.