Struggling with XML? Can't figure out the difference between an entity and a namespace? Fear not - our XML series has all the answers. This introductory article discusses the origins and design goals of XML, the basic rules of XML markup, and how to use elements and attributes in an XML document.
Every XML document must begin with a declaration that states the version of XML being used; this declaration is also referred to as the "document prolog."
This document prolog may also contain additional information, such as the document
encoding, and whether the document is to be viewed in combination with external DTDs or other entities (as explained above, a DTD lays down the format for an XML document and can be used to verify whether or not it is valid.) Consequently, the document prolog can sometimes look like this,
The document prolog also contains a document type declaration, used to specify
additional information about the document. This information typically includes the location of the DTD to use when validating the document (if there is one available), an optional list of entity declarations (more on this later), and the name of the root element of the document.
A document type declaration usually looks like this: