`  == Boolean attributes ==  It should be noted that shorthand boolean attributes omitting name-value pairs are invalid XML and will fail under the XML serialization of HTML5. HTML5 specifies that the presence of an attribute assigned a value of either the empty string or the literal attribute name is True, otherwise False. Since this is also compatible with the non-XML serialization, should it not be conventional to use valid XML in all HTML5 examples? This may be confusing for those who write exclusively XHTML and haven't seen the shorthand form. It seems rather common practice to write mostly XML syntax anyway except maybe xml:lang, with HTML5 supporting old crappy markup for legacy reasons. The HTML5 video tag for example has a number of boolean attributes for preloading video or adding controls etc:    The main point is that this way is more flexible and consistent even though it isn't strictly required for valid HTML.  http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#boolean-attribute    `