Special Edition Using XML, Second Edition

Well-Formed and Valid XML

In the first few chapters of this book, we have covered the various components that make up XML documents, such as elements and attributes. We've also taken a look at how those components come together to construct well-formed XML documents. You should now be familiar enough with the basics of XML to create your own well-formed XML documents without many problems, and now you should also be ready to move on to the next level of XML—valid XML documents.

Well-formed XML documents are appropriate for many applications; however, there are some instances where well-formed XML does not offer enough power to provide a good solution. In cases where entities are needed, or where you want to enforce specific rules about the document ...