Validating Your HTML
It is tempting, once you’ve finished writing the HTML, to start immediately on the CSS. After all, plain HTML is very ugly, and making it pretty with CSS is the fun part! But you should not skip validation. By making sure your pages are valid HTML, you ensure that they are accessible and that your CSS and scripts will work as you intend.
Luckily validating your HTML is easy and takes only a moment. Simply go to http://validator.w3.org and fill in the URL of the page. If it’s not live yet, you can validate your HTML by uploading a file or pasting it in as direct input. If you’ve been careful, you should see a green indicator, as in Figure 5.3, that tells you the document was successfully checked as HTML5.
FIGURE 5.3 A successfully validated web page.