When you are doing ANYthing, whether it's your job, your schoolwork, a hobby, or whatever — if you want to get better at it, consciously or not, you create games with rules to help you improve.
If you are playing a video game, the object is to make as many points as you can, gain the highest level you can, or gain that highest level as fast as you can. If you are learning to hand sew, it might be to make the stitches as straight and even as possible; it might be to make the stitches as small as possible; it might be to figure out a decorative way to make the stitches.
As a web designer, there are several mental games you can play play to improve your coding:
I looked for a good article on semantic web coding so you could better understand it. Most make my eyes glaze over. Here's some better articles:
To summarize them, in html 4, you only had divs to seperate elements, and they were a strictly visual division. But if we correctly code HTML5 using sections, articles, asides, etc., people and screen readers can determine what order text belongs in, and what information is grouped with what, to help them make sense of it, even if they can't see our beautiful design. If semantically correct, your page can be parsed by an outlining program, and the outline the program creates would look like the one you would create if you were outlining it yourself.
All four are good games to be playing while coding — how well can you use all of these when you're coding your web page?