var DOMPositionComparator = function(a,b){
	if(Prototype.Browser.IE){
		return a.sourceIndex - b.sourceIndex;
	}else if(Prototype.Browser.Gecko){
		return 3 - (a.compareDocumentPosition(b) & 6);
	}
};

var sortedFields = $$('img.L,img.M').sort(DOMPositionComparator);

This function will sort an array of DOM elements in order of the DOM position.  Useful when using calls such as $$("img.L,img.M") which doesn;t return a sorted element array.

It uses prototype but you can replace the Prototype.Browser stuff with anything else.

Sort Element Array by DOM Position

sort, array, DOM

JavaScript