code: def previousIndex(self, attrs):
          
          if not has_key(attrs, 'href'): return None
  
          i = -1
          for a in self.a:
              i += 1
              match = 0
  
              if has_key(a, 'href') and a['href'] == attrs['href']:
                  if has_key(a, 'title') or has_key(attrs, 'title'):
                          if (has_key(a, 'title') and has_key(attrs, 'title') and
                              a['title'] == attrs['title']):
                              match = True
                  else:
                      match = True
  
              if match: return i
docs: returns the index of certain set of attributes (of a link) in the
              self.a list
  
              If the set of attributes is not found, returns None