An XML document that has an associated document type declaration and complies with the constraints expressed in it. For more information visit the World Wide Web Consortium pages on XML.

XML documents are said to be "valid" when they include a reference to an internal or external Document Type Definition (DTD) file.

A well-formed Extensible Markup Language (XML) document that conforms to a specific set of constraints, usually defined in an XML Schema.

A well-formed XML document that conforms to a specific set of constraints, usually defined in an XML schema. “XML” bu'a qabeessa View

XML that conforms to the rules defined in the XML specification, as well as the rules defined in the DTD or schema. The parser must understand the validity constraints of the XML specification and check the document for possible violations. If the parser finds any errors, it must report them to the XML application. The parser must also read the DTD, validate the document against it, and again report any violations to the XML application. Because all of this parsing and checking can take time and because validation might not always be necessary, XML supports the notion of the well-formed document.

An XML document with elements and attributes that match the logical structure and data types defined in a particular schema.