scan is a CSS media feature that can be used to check what the scanning process (if any) of the output device is. The word scanning used in this context is not the same as with scanning a book or document into an image format using a scanner. Scanning here refers to the process in which an image is painted into a television (or other device) screen.
Identifies the current target for the event, as the event traverses the DOM. It always refers to the element the event handler has been attached to as opposed to event.target which identifies the element on which the event occurred.
Global attributes may be specified on all HTML elements, even those not specified in the standard. That means that any non-standard elements must still permit these attributes, even though using those elements means that the document is no longer HTML5-compliant. For example, HTML5-compliant browsers hide content marked as <foo hidden>...<foo>, even though <foo> is not a valid HTML element.