2.1.769 Part 4 Section 188.8.131.52, calculatedItem (Calculated Item)
a. The standard does not define restrictions on the value of the field attribute.
Office requires that the max value of the field attribute be less than the count of cacheField elements.
b. The standard does not specify usage of child pivotArea element.
In Office, pivotArea child element is used to specify cells to which the formula attributes apply.
c. The standard does not place any restrictions on the value for the formula attribute.
Office restricts the value of the formula attribute to be a Calculated Item Formula, as defined in Formulas ("[ECMA-376] Part 4 §3.17; Formulas").
d. The standard specifies that the field attribute indicates an index of the pivotField with which this calculated item is associated.
Office interprets the field attribute to specify an index of the cacheField with which this calculated item is associated.