When you create XML documents, you must work within two constraints: well-formedness and validity.
This module explains the well-formedess rules and how they are applied to create well-formed XML documents. The validity constraint is defined in this module and the technical details of creating valid XML documents will be discussed later in the course.
Extract XML Documents with PHP

By the end of the module, you will have the skills and knowledge necessary to:

1. Describe the concepts of well-formedness and validity
2. List the rules for creating a well-formed XML document
3. Determine the inherent structure of information within XML documents
4. Create a well-formed XML document
5. Work with mixed content
6. Add clarity and information to XML documents using comments, CDATA sections, and encoding

The next lesson describes the concepts of well-formedness and validity.