REgular LAnguage description for XML (RELAX) is a specification for describing XML-based languages.
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 JTC 1/SC 34 (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.