<Dd> Standardized in HTML 4.0 Transitional, obsolete in HTML5 . </Dd> <Dt> <iframe>... </ iframe> </Dt> <Dl> <Dd> An inline frame places another HTML document in a frame . Unlike an object element, an inline frame can be the "target" frame for links defined by other elements, and it can be selected by the user agent as the focus for printing, viewing its source, and so on . </Dd> <Dd> The content of the element is used as alternative text to be displayed if the browser does not support iframes . </Dd> <Dd> First introduced by Microsoft Internet Explorer in 1997, standardized in HTML 4.0 Transitional, allowed in HTML5 . </Dd> </Dl> <Dd> An inline frame places another HTML document in a frame . Unlike an object element, an inline frame can be the "target" frame for links defined by other elements, and it can be selected by the user agent as the focus for printing, viewing its source, and so on . </Dd>

What is the term for the number that identifies a particular element