//Author: Prof. Jeff
function makeChunkVisible( whatId ) {
  //document.getElementById( "firstTab" ).style.visibility = "hidden";
  document.getElementById( "secondTab" ).style.visibility = "hidden";
  document.getElementById( "thirdTab" ).style.visibility = "hidden";
  document.getElementById( "fourthTab" ).style.visibility = "hidden";
  
  //hide all command output images added
 // document.getElementById( "command1" ).style.visibility = "hidden";
  //document.getElementById( "command2" ).style.visibility = "hidden";
  //document.getElementById( "command3" ).style.visibility = "hidden";

  document.getElementById( whatId ).style.visibility = "visible";
}

function hoverOn( which ) {
  which.style.background = "#ffff00";
}

function hoverOff( which ) {
  which.style.background = "#ffffff";
}