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;
}