We've learned a lot of the syntax and rules of creating XML documents at the element and character data levels. It's time to move on to the next level: actually giving your document structure.
The W3C has a lot of rules about how to structure your document in a way to make it well formed, and I'm going to take a look at those rules here. In this chapter, I'm going to talk about only standalone documents; in the next chapter, we'll see that we have to adjust these points somewhat for documents that have a DTD.
If you have doubts about whether your XML document is well formed, use an online XML validator, such as the excellent one hosted by the Brown University Scholarly Technology ...