HTML attributes are special words used inside the opening tag to control the element's behaviour. HTML attributes are a modifier of an HTML element type. An attribute either modifies the default functionality of an element type or provides functionality to certain element types unable to function correctly without them. In HTML syntax, an attribute is added to an HTML start tag.
Several basic attributes types have been recognized, including: (1) required attributes, needed by a particular element type for that element type to function correctly; (2) optional attributes, used to modify the default functionality of an element type; (3) standard attributes, supported by many element types; and (4) event attributes, used to cause element types to specify scripts to be run under specific circumstances.