What about images and other multimedia elements we see and hear as part of our web browser displays? Aren’t they part of the HTML document? No. The data that comprises digital images, movies, sounds, and other multimedia elements that may be included in the browser display is in files separate from the main HTML/XHTML document. You include references to those multimedia elements via special tags. The browser uses those references to load and integrate other types of documents with your text.
We didn’t include any special multimedia references in the previous example simply because they are separate, nontext documents that you can’t just type into a text processor.