pg_range stores information about range types. This is in addition to the types' entries in
OID of the range type
OID of the element type (subtype) of this range type
OID of the multirange type for this range type
OID of the collation used for range comparisons, or zero if none
OID of the subtype's operator class used for range comparisons
OID of the function to convert a range value into canonical form, or zero if none
OID of the function to return the difference between two element values as
rngcollation, if the element type is collatable) determines the sort ordering used by the range type.
rngcanonical is used when the element type is discrete.
rngsubdiff is optional but should be supplied to improve performance of GiST indexes on the range type.