6.1. Elements

The nodes shown in Listing 6-1 are called elements, and they closely resemble HTML tags. And like HTML tags, start tags begin with < and end tags begin with </. However, unlike HTML tags, all XML tags must either have a closing tag or be self-closing or empty elements. Self-closing tags are recognizable by the ending />. If the forward slash was omitted, the document would not be a well-formed XML document. In addition to all elements being either closed or self-closing, the tags must always match up in order. This means that the XML document in Listing 6-2 is well formed, whereas the XML document in Listing 6-3 is not well formed.

Listing 6-2. A Well-Formed XML Document

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <one> <two> <three> <four/> </three> </two> </one>

Listing 6-3. A Document That Is Not Well Formed

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <one> <two> <three> <four/> </two> </three> </one>

So far, we have covered elements that contain either other elements or empty elements, leaving the question of what elements that contain actual data look like. Using the XML from Listing 6-1 as a starting point, you can see that the answer is not very different. Listing 6-4 shows what elements that contain text data look like.

Listing 6-4. An XML Document with Text Data

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <library> <book> <series>The Lord of the Rings</series> <title>The Fellowship of the Ring</title> <author>J.R.R. Tolkien</author> </book> <book> <series>The Lord of the Rings</series> <title>The Two Towers</title> <author>J.R.R. Tolkien</author> </book> <book> <series>The Lord of the Rings</series> <title>The Return of the King</title> <author>J.R.R. Tolkien</author> </book> </library>

One thing to remember is that elements aren't limited to containing either other elements or text data; they can do both at the same time. In fact, there is even a way for empty elements to contain text data through the use of attributes.