A element must appear at the top level. A element should not have more than one head element. A element should not have more than one body element. A element must only appear at the top level. A element should be a child of the smil element. A element should only contain the elements layout, switch or meta. A element should have a name attribute. A element should have a content attribute. A element can only appear in a head element. A element should not have any content. A element can only appear in a head or switch element. A element in the head can only contain layout elements. A must be in a layout element. A should be empty. It should not have any subelements. A element should be a child of the smil element. A element can only have container content. A element can only have container content. Only anchor elements are allowed as subelements of media object elements. A element may only be inside the elements par, switch or seq. A element should have an href element. A element should have an href element. A Media Object attribute should only be on a Media Object Element. A element cannot have an ID attribute. The show attribute on a element should have one of the values replace, new or pause. A skip-content attribute on a element can only have a value of true or false. In the element the attribute fit can only have values hidden, fill, meet, scroll or slice.