//function to change some styles (eg background colour) of an element when it is given focus in IE
function setFocusStyle(element_id)
{
//no action needed for Opera and Firefox, these browsers handle the style changes
//associated with changes of focus but 
//the CSS pseudo class input:focus is not supported by IE7 and below
//so change the class input to focus_style
	if(document.getElementById(element_id).className.backgroundColor === undefined)
		{
		document.getElementById(element_id).className = "focus_style";
		}
}