code: def _indexOfEndTag(istack):
      
      if len(istack) <= 0:
          return 0
  
      if not istack[0].isOpeningTag():
          return 0
  
      cnt = 0
      opener = istack[0]
      for index, el in enumerate(istack[1:]):
          if el.isOpeningTag() and \
             el.getTagName().lower() == opener.getTagName().lower():
              cnt += 1
  
          elif el.isEndTagTo(opener):
              if cnt == 0:
                  return index + 1
  
              cnt -= 1
  
      return 0
docs: Go through `istack` and search endtag. Element at first index is considered
      as opening tag.
  
      Args:
          istack (list): List of :class:`.HTMLElement` objects.
  
      Returns:
          int: Index of end tag or 0 if not found.