windowed elements and z-index

  Ok, windowed elements such as <select> and <iframe> cannot be controlled with z-index
but, shouldn't they be dependent on their parent's z-index? I was expecting a <select>
element to behave according to it's container's z-index when I expand a DHTML menu on top
of it, instead of having to alter it's display value every time the menu unfolds... can
someone please explain to me why?

Manos