2.1.1518 Part 1 Section 184.108.40.206, pt (Numeric Point)
a. 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.
b. 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.
c. The standard states that the idx attribute is the index of the series in the collection.
In Office, the idx attribute is the index of the points in the collection.