An XML document that adheres to syntax rules specified by XML 1.0…

An XML document that follows all XML 1.0 syntax rules , so that both its physical structure and logical structure are correct (proper nesting, required start and end tags, correct attribute format and structure), is called a well-formed XML document . A valid XML document is one that is well-formed and also follows the rules of a DTD or schema, but the question is only about following syntax rules, so the correct term here is well-formed .