var currentlyVisible = null;

function toggleVisibility( which ) {
  if( currentlyVisible == null ) {
    currentlyVisible = document.getElementById( "description" );
  }
  currentlyVisible.style.visibility = "hidden";
  currentlyVisible = document.getElementById( which );
  currentlyVisible.style.visibility = "visible";
}

function hoverOn( what ) {
  what.style.background = "#ffff00";
  what.style.cursor = "pointer";
}

function hoverOff( what ) {
  what.style.background = "#ffffff";
  what.style.cursor = "auto";
}