function fontChanger(operation, divName, defaultSize) {
  // Setting up array of tags, use as many as you want.
  var tagList = new Array('p', 'th', 'td', 'li', 'span');
  var defaultLine = (parseInt(defaultSize) + 3);
  // Looping through array of tags
  for(var i = 0; i < tagList.length; i++) {
    var allTags = document.getElementById(divName).getElementsByTagName(tagList[i]);
    for(var j = 0; j < allTags.length; j++) {
      // If a size is set, use it, else use defaults
      var size = (allTags[j].style.fontSize ? parseInt(allTags[j].style.fontSize.replace('px', '')) : parseInt(defaultSize));
      var line = (allTags[j].style.lineHeight ? parseInt(allTags[j].style.lineHeight.replace('px', '')) : parseInt(defaultLine));
      // Perform action, re-write style
      allTags[j].style.fontSize = (size += (operation == 0 ? 1 : -1)) + 'px';
      allTags[j].style.lineHeight = (line += (operation == 0 ? 1 : -1)) + 'px';
    }
  }
}