Didn't create the language, but had to implement a parser for RELAX NG Compact[0] years ago (in PHP!!). It was to provide a client the flexibility they "needed

Didn't create the language, but had to implement a parser for RELAX NG Compact[0] years ago (in PHP!!). It was to provide a client the flexibility they "needed" for data validation specifications. It was a mess. We suggested many alternative routes, but the client insisted on this. We did make the saner decision to go with an already-established markup language. We couldn't even do the full XML version, as the client didn't want to "do XML". [0] http://relaxng.org/compact-tutorial-20030326.html http://relaxng.org/compact-tutorial-20030326.html