The HTML block is flexible and can incorporate a variety of functions and uses in the content area. It has the standard Moodle HTML editor for formatting text, adding images or creating links, switching to code view and allows any valid HTML markup to be used. This enables embedding video, sounds, Flash, and other files which can add unique elements to a course or site page.
If you see a gauge icon on any of the files in your HTML block, your institution uses Ally to measure the accessibility of course content. To learn more, see Ally help for instructors.
More on the HTML block on the Moodle website (may be available in English only)