function TabClass(container, docwin) {
  /* define required members */

  // data members
  this.container = container;						  // [object node] element that holds all of the content elements (iframe)
  this.docwin = docwin;                               // [object node] node that holds the iframe (or object) which displays the document content.  could be displayed in this node, not child
  this.indice = null                                  // [number] should point to itself in tab.arr[]
  this.node = null;                                   // [object node] should refer to the tab element
  this._closed = false;                               // [boolean] true if this tab has been closed
  this._label = null;                                 // [string] used to remember first label before changes
  
  // empty methods that should be declared in child class
  this.setActive = new Function();
  this.setInActive = new Function();
  this.positionElements = new Function();

  // methods
  this.open = TabClass_OpenTab;
  this.close = TabClass_CloseTab;
  this.isOpen = TabClass_IsOpen;
  this.setTitle = TabClass_SetTitle;
  this.proportionate = TabClass_ProportionateNodeSize;
}