And point it to the ref guide like we have others?

At minimum we need to reconcile these warnings with the use of ord and
rord in lots of examples in the reference guide. Are these are
obsolete with docValues?

WARNING: as of Solr 1.4, ord() and rord() can cause excess memory use
since they must use a FieldCache entry at the top level reader, while
sorting and function queries now use entries at the segment level.
Hence sorting or using a different function query, in addition to
ord()/rord() will double memory use.