2.1.794 Part 1 Section 188.8.131.52, reference (Reference)
a. The standard defines @field (Field Index) values range as unsignedInt and says a value of -2 indicates the data field.
Office uses the value 4294967294 (a valid unsignedInt) to specify the data field and the @v in the x elements represent indices into the dataFields collection.
b. The standard defines @field values range as unsignedInt.
Office requires that if the pivotArea@cacheIndex is 0, then the value shall be a valid index in the pivotFields in the pivotTable, and, unless byPosition is 1, @v in the x elements represent indices into items collection of the pivotField.
c. The standard states the that values for the field attribute are defined by the XML Schema unsignedInt datatype.
Office requires that if the pivotArea@chacheIndex is 1 the value shall be a valid index in the cacheFields in the pivot cache and the v attribute in the x elements represent indices into sharedItems collection of the cacheField.