Strategic XML

Creating a Valid Document

The document in Listing 2.2 can be successfully parsed by any XML parser because it doesn't violate any of XML's well-formedness constraints. But just because a document is well-formed doesn't mean that the contents are useful for a particular application. For instance, what if the restaurant owner made a mistake when he was updating the menu and accidentally gave an item two prices:

<item id="L3">
  <name>Pepsi</name>
  <price>$1.00</price>
  <price>$.75</price>
</item>

The document would still be parsed without generating errors, because it is still well-formed XML. But in the context of the actual application, having an item with two prices is definitely an error. At best, this would generate incorrect output (a menu ...