// show_element():
// toggles between visible and unvisible using display:block / display: none-CSS-property.
// id="id" and style="display: none;" have to be defined. in the HTML-element

function show_element(id){
	if(document.getElementById(id) != null){
		var el = document.getElementById(id);
		
		if (el.style.display == 'block') {
			el.style.display = 'none';
		} else {
			el.style.display = 'block';
		}
	}
}