This appendix contains XML reference material. It is divided into three main parts: 1. XML BNF Grammar 2. Well-Formedness Constraints 3. Validity Constraints The XML BNF grammar reference section shows you how to read a BNF Grammar and includes the BNF rules for XML 1.0 and examples of the XML 1.0 productions. The wellformedness constraints reference section explains what a well-formedness constraint is and lists the productions associated with the well-formedness constraints. The validity constraints reference section explains what a validity constraint is and lists and explains all of the validity constraints in the XML 1.0 Standard. XML BNF Grammar According to the XML 1.0 specification, an XML document is well-formed if: 1. Taken as a whole it matches the production labeled document. 2. It meets all the well-formedness constraints given in this specification. 3. Each of the parsed entities which is referenced directly or indirectly within the document is well-formed. This section is designed to help you understand the first of those requirements and more quickly determine whether your documents meet that requirement.