getElementsBySelector does'nt return a document-ordered array

This code may help you. I lifted it from PPK's QuirksMode.org and stuck it in a generic function:

function sortByDocOrder(list) {
	var testNode = list[0];
	// IE doc-order
	if (testNode.sourceIndex) {
		list.sort(function (a,b) {
			return a.sourceIndex - b.sourceIndex;
		});
	}
	// W3C doc-order
	else if (testNode.compareDocumentPosition) {
		list.sort(function (a,b) {
			return 3 - (a.compareDocumentPosition(b) & 6);
		});
	}
}

Thanks for pointing this out. I've updated the documentation.