Structure of XML document

How does the XML structure is defined?
XML document will have a structure which has to be defined before we can create the documents and work with them. The structural rules can be defined using many available technologies, but the following are popular way of doing so-

• Document Type Definition (DTD)
• Schema

What is the structure of XML document ?

Figure 1: XML Structure

What is a Processing Instruction in XML?
A ProcessingIntruction is the information which we would like to give to application. Through a ProcessingInstruction an application would get idea about how to process the document. A ProcessingInstruction can appear anywhere and any no. of times in a document.