It’s important to have a basic understanding of DITA element classes because you’re going to use them to create variables that pull metadata from your map for use in headers and footers. You also use them anywhere else within your plugin where you need to identify a specific element.
If you’ve worked with XPath or XSL before, you might be used to selecting elements by name. DITA selects elements differently. It uses the class attribute rather than the element name. All DITA elements have a class attribute.