/// The native lucene index order is used to assign an ordinal value for each field value. ///
/// Field values (terms) are lexicographically ordered by unicode value, and numbered starting at 1.
///
/// Example of reverse ordinal (rord):
///
If there were only three field values: "apple","banana","pear"
///
then rord("apple")=3, rord("banana")=2, ord("pear")=1
///
/// WARNING: /// rord() depends on the position in an index and can thus change /// when other documents are inserted or deleted, /// or if a MultiSearcher is used. /// ///
/// WARNING: The status of the search.function package is experimental. /// The APIs introduced here might change in the future and will not be /// supported anymore in such a case. /// ///