Fires after a script adds, removes, or changes the value of an element's attribute. Adding or removing an attribute must be done by the  setAttribute( ) and  removeAttribute( ) methods, but changing an existing attribute may be accomplished either by the setAttribute( ) method or assigning a new value to an element object's property that corresponds to an attribute. Numerous event object properties convey details about the event. See the following properties of the event object: attrName, attrChange, prevValue, newValue, and relatedNode.