下文摘自M$ MSDN http://msdn.microsoft.com/workshop/author/dhtml/reference/properties/zindex.aspResPositive z-index values are positioned above a negative (or lesser value) z-index. Two objects with the same z-index are stacked according to source order. A positive value positions the element above text that has no defined z-index, and a negative value positions it below. Set this parameter to null to remove the attribute.The zIndex property only applies to objects that have the position property set to relative or absolute.The property does not apply to windowed controls, such as select objects.As of Microsoft Internet Explorer 5.5, the iframe object is windowless and supports the zIndex property. In earlier versions of Internet Explorer, the iframe object is windowed and, like all windowed controls, ignores the zIndex property. If you maintain Web pages that were designed for earlier versions of Internet Explorer that do not support the zIndex property, you might want to redesign the pages, especially if the pages contain iframe objects that are stacked on top of windowed controls, such as select objects. You can use the visibility attribute to hide windowed controls that you want an iframe object to overlap. You can also position windowed controls so that iframe objects do not overlap them.Input from pointing devices, such as the mouse, does not penetrate through overlapping elements even if the elements are not visible. This is also true for positioned elements with a negative z-index unless: The parent is a scrolling container (that is, its overflow property is set to auto or scroll). The parent is positioned (that is, its position property is set to absolute or relative).你还是从其他方法考虑吧？例如在js加上对select的visible/hidden
1.你在DIV里设置了position和z-index那么iframe就没有必要设置了,
2.设置z-index大于0就不会被select等覆盖了.
http://msdn.microsoft.com/workshop/author/dhtml/reference/properties/zindex.aspResPositive z-index values are positioned above a negative (or lesser value) z-index. Two objects with the same z-index are stacked according to source order. A positive value positions the element above text that has no defined z-index, and a negative value positions it below. Set this parameter to null to remove the attribute.The zIndex property only applies to objects that have the position property set to relative or absolute.The property does not apply to windowed controls, such as select objects.As of Microsoft Internet Explorer 5.5, the iframe object is windowless and supports the zIndex property. In earlier versions of Internet Explorer, the iframe object is windowed and, like all windowed controls, ignores the zIndex property. If you maintain Web pages that were designed for earlier versions of Internet Explorer that do not support the zIndex property, you might want to redesign the pages, especially if the pages contain iframe objects that are stacked on top of windowed controls, such as select objects. You can use the visibility attribute to hide windowed controls that you want an iframe object to overlap. You can also position windowed controls so that iframe objects do not overlap them.Input from pointing devices, such as the mouse, does not penetrate through overlapping elements even if the elements are not visible. This is also true for positioned elements with a negative z-index unless: The parent is a scrolling container (that is, its overflow property is set to auto or scroll).
The parent is positioned (that is, its position property is set to absolute or relative).你还是从其他方法考虑吧？例如在js加上对select的visible/hidden