Get all elements of particular type and class without jQuery

I wanted some nice function, that will return all DOM elements:

• of given element type (name),
• contained in another element,
• having given class.

For example, to get all list items (<li>) with some class, but inside <ol> rather than in entire DOM tree.

I failed to find one of such, so I wrote it.

Here is the code. This function will seek all child elements (all child nodes) of elementType type, contained in rootElement, but return only these, that has className class.

var getElementsByClassName = function (rootElement, elementType, className)
{
    var arrElements = (elementType == "*" && rootElement.all)? rootElement.all : rootElement.getElementsByTagName(elementType);
    var arrReturnElements = new Array();

    className = className.replace(/-/g, "\-");

    var oRegExp = new RegExp("(^|\s)" + className + "(\s|$)");
    var oElement;

    for(var i=0; i<arrElements.length; i++)
    {
        oElement = arrElements[i];
        if(oRegExp.test(oElement.className))
        {
            arrReturnElements.push(oElement);
        }
    }

    return (arrReturnElements)
}

This task is more then easy (obvious?) with jQuery. But for people/projects that doesn’t use jQuery, this function may be handy.