function changeView(className, idNum, tag, parentID) {
  var testClass = new RegExp("(^|\s)" + className + "(\d+(\s|$))");
  var showElement = new RegExp("(^|\s)" + className + idNum + "(\s|$)");
  var tag = tag || "*";
  var elementID = document.getElementById(parentID) || document;
  var elements = elementID.getElementsByTagName(tag);
  var returnClasses = [];
  var current;
  var length = elements.length;
  for(var i=0; i<length; i++){
    current = elements[i];
    if(testClass.test(current.className)){
      returnClasses.push(current);
    }
  }
  length = returnClasses.length;
  for(var i=0; i<length; i++){
    current = returnClasses[i];
    if (showElement.test(tabs.className)) {
      current.style.display = 'block';
    } else {
      current.style.display = 'none';
    }
  }
}

##### HTML Snippet that calls function #####

        <div id="storybox">
          <ul class="tabs">
            <li class="tab_01"><a href="#pop1" onclick="changeView("tab_", "01", "*", "storybox"); return false;" title="">Next</a></li>
            <li class="tab_02"><a href="#pop2" onclick="changeView("tab_", "02", "*", "storybox"); return false;" title="">Prev</a></li>
          </ul>
          <div class="tabcontent tab_01">
            ...
          </div>
          <div class="tabcontent tab_02">
            ...
          </div>
        </div>