Later, when we get into video, you may see some attributes with no value assigned. These are boolean attributes, which means they either exist or they don’t, which determines whether they are true or false. If they are present, it is assumed they are true. One common place these are seen is in the <video> tag. You can optionally include player controls, or remove the attribute altogether, to have a chromeless video play.
In the above example, the preload, controls and loop attributes do not assign a value (there is no equals symbol). If they are present, then they set those properties of the video.