This document describes how to specify XML structures through XML itself. It is about Simba, a little but powerful XML dialect that should enable developers to quickly author XML document types without the complexity of using the XML DTD syntax, nor the weight of the official W3C XML Schema language. Simba is an XML Schema language that aims to provide just enough syntactic sugar to enable a formal and strongly typed definition of standard XML constructs. Simba is in particular useful to describe XML structures for use in protocols/messaging.