ISO/IEC 19757 defines a set of Document Schema Definition Languages (DSDL) that can be used to specify one or more validation processes performed against Extensible Markup Language (XML) documents.

ISO/IEC 19757-7:2009 specifies a Character Repertoire Description Language (CREPDL); a CREPDL schema describes a character repertoire. ISO/IEC 19757-7:2009 introduces kernels and hulls of repertoires, then specifies the syntax of CREPDL schemas and the semantics of a correct CREPDL schema; the semantics specify when a character is in a repertoire described by a CREPDL schema. ISO/IEC 19757-7:2009 defines CREPDL processors and their behaviour. Finally, it describes differences of conformant CREPDL processors, and provides examples of CREPDL schemas.