var MARKS_IMG_PRE = "images/proof_mark_";
var MARKS_TEXT    = new Array("", "Delete", "Delete line space", "New paragraph", "Insert space", "Period", "Comma", "Colon", "Semicolon", "Apostrophe");

function getRandom(max, min, dec) {
  if (!max) max = 1;
  if (!min) min = 0;
  if (!dec) dec = 0;
  var decFactor = Math.pow(10, dec);
  var num = Math.round(Math.random() * ((max-min) * decFactor)) / decFactor + min;
  var str = num.toString();
  var decPos = str.indexOf(".");
  return (decPos == -1) ? num : parseFloat(str.substring(0, decPos+dec+1));
}

function winLoad() {
  var markObj = document.getElementById("proofMark");
  var num = getRandom(MARKS_TEXT.length-1, 1);

  if (markObj) {
    markObj.src = MARKS_IMG_PRE + num +".gif";
    markObj.alt = MARKS_TEXT[num];
  }
}

window.onload = winLoad;