Grasping abstract concepts like the ones we've discussed in our first two lessons isn't always easy. It takes some study and repetition, as well as real-world experience. You'll start getting the real-world experience in Lesson 3. For study and repetition, it often helps to see the same concepts explained in a different way and in a different context. So, for this lesson, I'd like you to look at the first two items in the Supplementary Material section.

The first article, titled Selectutorial, takes you step-by-step through the terms and concepts you learned in Lessons 1 and 2. It also gets into some topics you'll see in upcoming lessons.

The second article, titled W3C Selectors, is the World Wide Web Consortium's official specification on how CSS selectors work. In typical W3C fashion, the information is very terse and technical. But the W3C is the root of all factual information about CSS and XHTML. So, it can't hurt to read their version of the facts, and maybe bookmark the page or add it to your browser favorites. As your knowledge of CSS and XHTML grows, so will your ability to understand the W3C documentation and use it as a valuable resource.