code: public ElemTemplateElement getPreviousSiblingElem()
    {
  
      ElemTemplateElement walker = getParentNodeElem();
      ElemTemplateElement prev = null;
  
      if (walker != null)
        for (walker = walker.getFirstChildElem(); walker != null;
                prev = walker, walker = walker.getNextSiblingElem())
        {
          if (walker == this)
            return prev;
        }
  
      return null;
    }
docs: Get the previous sibling (as a Node) or return null.
  Note that this may be expensive if the parent has many kids;
  we accept that price in exchange for avoiding the prev pointer
  TODO: If we were sure parents and sibs are always ElemTemplateElements,
  we could hit the fields directly rather than thru accessors.
  
  @return This node's previous sibling or null