elm.insertAdjacentHTML( 'BeforeEnd', '<span style="visivility:hidden;line-height:1;">X</span>' );
elm = elm.children[ elm.children.length - 1 ];
v = elm.offsetHeight;
elm.insertAdjacentHTML( 'BeforeEnd', '<span style="visivility:hidden;line-height:1;">X</span>' );
elm = elm.children[ elm.children.length - 1 ];
v = elm.offsetHeight;