XML is a "syntax franca" in the computer industry, like English and mathematics are a "lingua franca" in publications in the field of computing science. Theories, formulas and logic rules can be stated in a suitable XML vocabulary. But such an XML encoding is only for the syntax, it is not capturing dynamics, necessary for the semantics of a formalism. At CWI I developed an XML extension called RML that makes it possible to define such semantics. More specifically, with RML it is possible to define rule based XML transformations. With XML+RML we can freely define XML languages and rules for formal semantics. These semantics are executable with the help of the RML tools that have been developed, thus providing the possibility of experimental analysis of a formal semantics serving as the mathematical basis for software technoloy. After an introduction to XML and RML I will show how we applied XML+RML to various topics like propositional logic, UML and business processes modelling. The last part of the talk will be a short workshop.