XML must be “well-formed”
For the data contained in an XML document to be parsed correctly, its markup must be well-formed, meaning that properly nested and nonabbreviated starting and ending tags are used.
- This well-formedness provides the encapsulation mechanism allowing designated sections of the data to be accessed programmatically.
- It is important to remember that XML is a markup language, not a programming language
Scenario #1: the server offers the XML document without its DTD, the parser does a syntax check, and the DTD follows if the XML document is “well-formed”
Scenario #2: the server checks the XML document against its DTD (“validity”) before sending the document to the client