var currentDisplayedElementId;
var visible = 'block';
var hidden = 'none';
  
function displayElement(elementId)
{
	element = document.getElementById(elementId);
	
	hideCurrentElement();
	
	element.style.display = (element.style.display == visible ? hidden : visible);

	currentDisplayedElementId = elementId;
}

function hideCurrentElement()
{
	if (currentDisplayedElementId)
	{
		currentElement = document.getElementById(currentDisplayedElementId);
		currentElement.style.display = hidden; 
	}
}