REgular LAnguage description for XML (RELAX) is a specification for describing XML-based languages. A description written in RELAX is called a RELAX grammar.
RELAX Core has been approved as an ISO/IEC Technical Report 22250-1 in 2002 (ISO/IEC TR 22250-1:2002).[1] It was developed by ISO/IEC JTC1/SC34 (ISO/IEC Joint Technical Committee 1, Subcommittee 34 - Document description and processing languages).[2][3]
RELAX was designed by Murata Makoto.
In 2001, an XML schema language RELAX NG was created by unifying of RELAX Core and James Clark's TREX.[4][5][6] It was published as ISO/IEC 19757-2 in 2003.[7]