R
- RailML: language for interoperability in railway industry applications.
- RAML: vocabulary for describing relational algebra expressions
- RDFa
- RecipeML
- Regular Language description for XML
- RELAX NG: a schema language
- REML : Recipe Exchange Markup Language, non-proprietary (BSD license), English-based
- Remote Telescope Markup Language
- Resource Description Framework: a metadata model based upon the idea of making statements about resources
- RoadXML: file format for driving simulator database.
- RSS (file format)
- RSS enclosure
- RuleML: a markup language for rules
Read more about this topic: List Of XML Markup Languages