This book is for Web users learn- ing to create their own Web pages using HTML, the standard tagging language for the World Wide Web. .disabled-checkbox { opacity: 0.5; /* Reduce the opacity of the checkbox */ cursor: not-allowed; /* Change the cursor to indicate that the checkbox is disabled */ pointer-events: none; /* Disable pointer events to prevent user interaction */. element. I found a pretty good browser extension called Headings Map that is available for both Chrome and Firefox. You might even make the search engines happier too. Search engines are able to better understand what information each section holds, which could potentially improve SEO. It is a sub-section that requires context from its parent sectioning element to make sense. In the same way that