Years ago, I co-founded a subgroup of XML-DEV, called SML-DEV, along with a substantial number of XML experts to work on simplifying XML and XML-based specs.  SML-DEV group is inactive now, but while it was active, some members of SML-DEV started working on YAML (YAML Ain't Markup Language) and eventually formed an independent group, led by Clark Evans of Axista, to concentrate on YAML.

The YAML has now come a long way and now they have a score of implementations along with a mature spec.  I recommend you to check it out.

Simon St. Laurent writes in YAML Ain't Markup Language:

Long ago, YAML was "Yet Another Markup Language", part of the activity which emerged from the SML-DEV mailing list's work on XML simplification. They've changed the name and sharpened the focus on serialization, wisely severing their ties to markup practice per se, which covers a much broader set of issues.