OptionalbaseThe field showDataAs compares against, by index.
OptionalbaseThe item of baseField showDataAs compares against: by index, or the one before or
after each item.
The field summarized, by index.
OptionalnumberThe number format of its values: a format code, or a built-in format's id; absent, General.
OptionalshowHow the value is shown, as OOXML spells it (percentOfTotal, difference,
percentOfParentRow, rankAscending…); absent, as is.
OptionalsubtotalThe function, as OOXML spells it; absent, sum.
A value of a pivot table: a field of the cache summarized by a function.