You could potentially make it work by manually setting the CSS z-index (there are some places where dynamically calculating this property is necessary) of the second dialog, but I’d recommend reevaluating your needs and refactoring. This has never worked in Web 2.0 to my knowledge as I brought it up in an early build and I’m sure there are other threads around here about that.
It does appear to work by load order for simple dialogs, in my testing, but the z-index of the dialogs doesn’t seem to be calculated and applied at show, so that makes it unreliable. You can enforce it with something like this, before calling Show on the dialog:
this could work also for webmessagedialog I tried using “_dialog” instead of “_modal”
but it doesn’t
seems the webmessagedialog has no ID on the html side ?