Moving select options with jQuery

I wanted to move select options up/down on a click of a button. The following jQuery snippet does exactly that, if you want to put in some moveby variable (delta) execute this stuff within a for loop

#UPDATE My implementation was valid ages & jQueries ago, thanks to imants.horsts for updated solution

$.fn.moveSelectedUp = function() {
var selectedOptions = $(this).selectedOptions();
var prev = $(selectedOptions).first().prev();
$(selectedOptions).insertBefore(prev);
}

$.fn.moveSelectedTop = function() {
var selectedOptions = $(this).selectedOptions();
var first = $(this).children("option").not(":selected").first();
$(selectedOptions).insertBefore(first);
}

$.fn.moveSelectedBottom = function() {
var selectedOptions = $(this).selectedOptions();
var last = $(this).children("option").not(":selected").last();
$(selectedOptions).insertAfter(last);
}


This solution is tested in FF3 & IE6/7, should work elsewhere as well