Copyright (C) 2001 Rick Jellife. Freely and openly available under zlib/libpng license. This schema is open: it only considers elements in the Schematron namespce. Elements and attributes from other namespaces can be used freely. This schema does not assume that the Schematron schema is the top-level element. This schema uses conservative rules (e.g. no use of key()) to work with incomplete XSLT-based implementations. These rule establish the smallest possible Schematron document. These rules may be handy for beginners with starting documents. Rules defining occurrence rules for Schematron elements and their required attributes. Note that for attributes, it is not that the attribute is being tested for existance, but whether it has a value. Some elements require certain children or attributes. Other elements require certain parents. Schematron can represent both these kinds of coupling. These rules specify which elements each attribute can belong to, and what they mean.