XML - Wikipedia
https://en.wikipedia.org/wiki/XMLThe material in this section is based on the XML Specification. This is not an exhaustive list of all the constructs that appear in XML; it provides an introduction to the key constructs most often encountered in day-to-day use. Character An XML document is a string of characters. Almost every legal Unicode character may appear i…
Well-formed document - Wikipedia
en.wikipedia.org › wiki › Well-formed_documentA valid XML document is defined in the XML specification as a well-formed XML document which also conforms to the rules of a Document Type Definition (DTD). According to JavaCommerce.com XML tutorial, "Well formed XML documents simply markup pages with descriptive tags. You don't need to describe or explain what these tags mean.