说明：  What is XML? XML is a markup language for documents containing structured information. Structured information contains both content (words, pictures, etc.) and some indication of what role that content plays. A markup language is a mechanism to identify structures in a document. The XML specification defines a standard way to add markup to documents.
(What is XML? XML is a markup language for documents containing structured information.Structured information contains both content (words, pictures, etc.) And some indication of what role that content plays. A markup language is a mechanism to identify structures in a document . The XML specification defines a standard way to add markup to documents.)