Chapter 3. Valid Documents: Creating Document Type Definitions

In the previous chapter, we saw all about creating well-formed XML documents. However, there's more to creating good XML documents than the simple (although essential) requirement that they be well formed . Because you can create your own tags when you create an XML application, it's up to you to set their syntax. For example, can a <HOUSE> element contain plain text or only other elements such as <TENANT> or <OWNER> ? Must a <BOOK> element contain a <PAGE_COUNT> element, or can it get by without one? It's up to you to decide. Making sure documents have been written using your XML syntax is not only good for making sure your documents are legible, it can also be essential for programs that deal with documents via code.