Real World XML

Creating Document Type Declarations

You define the syntax and structure of elements using a document type definition (DTD), and you declare that definition in a document using a document type declaration. We've seen that you use the <!DOCTYPE> element to create a document type declaration. This element can take many different forms, as you see here (here, URL is the URL of a DTD, and rootname is the name of the root element); we'll see all these forms in this chapter:

• <!DOCTYPE rootname [DTD]>

• <!DOCTYPE rootname SYSTEM URL>

• <!DOCTYPE rootname SYSTEM URL [DTD]>

• <!DOCTYPE rootname PUBLIC identifier URL>

• <!DOCTYPE rootname PUBLIC identifier URL [DTD]>

To use a DTD, you need a document type declaration, which means that you need a <!DOCTYPE> element. ...