2.1.828 Part 4 Section 184.108.40.206, x (Member Property Index)
a. The standard states the values for the v attribute are defined by the XML Schema int datatype.
Office requires that the v attribute be greater than or equal to -1 and less than the corresponding sharedItems count. A value of -1 specifies that there is no value for this member property.
b. The standard describes x as an array of indexes.
Office expects that x represents an index to the cached member property value.
c. The standard does not provide complete information on which cacheField's shared item table is indexed by @v.
Office assumes that @v is the 0-based index into the shared items table of the member property pointed by @mpMap. The Nth @mpMap used for Nth x element (the parent of @v).
d. The standard says @v represents an index to shared items table.
Office specifies that if the parent of this element is i, then v shall be specified by the specification for i ("[ECMA-376] Part 4 §220.127.116.11; i").