/** Toggle an element's display style between "block" and "none". */
function toggleDisplay(id) {
  	var elm = document.getElementById(id);
	elm.style.display = (elm.style.display=="block")?"none":"block";
}

/** Display an element as a block. */
function show(id) {
	var elm = document.getElementById(id);
	if (elm == null) alert("Can't show unknown element '" + id + "'!");
	elm.style.display = "block";
}

/** Change display style to "none". */
function hide(id) {
	var elm = document.getElementById(id);
	if (elm == null) alert("Can't hide unknown element '" + id + "'!");
	elm.style.display = "none";
}