code: def _match(self, pred):
          
          if not pred:
              return True
          # Strip off the [ and ]
          pred = pred[1:-1]
          if pred.startswith('@'):
              # An attribute predicate checks the existence (and optionally value) of an attribute on this tag.
              pred = pred[1:]
              if '=' in pred:
                  attr, value = pred.split('=', 1)
                  if value[0] in ('"', "'"):
                      value = value[1:]
                  if value[-1] in ('"', "'"):
                      value = value[:-1]
                  return self.attrs.get(attr) == value
              else:
                  return pred in self.attrs
          elif num_re.match(pred):
              # An index predicate checks whether we are the n-th child of our parent (0-based).
              index = int(pred)
              if index < 0:
                  if self.parent:
                      # For negative indexes, count from the end of the list.
                      return self.index == (len(self.parent._children) + index)
                  else:
                      # If we're the root node, the only index we could be is 0.
                      return index == 0
              else:
                  return index == self.index
          else:
              if '=' in pred:
                  tag, value = pred.split('=', 1)
                  if value[0] in ('"', "'"):
                      value = value[1:]
                  if value[-1] in ('"', "'"):
                      value = value[:-1]
                  for c in self._children:
                      if c.tagname == tag and c.data == value:
                          return True
              else:
                  # A plain [tag] predicate means we match if we have a child with tagname "tag".
                  for c in self._children:
                      if c.tagname == pred:
                          return True
          return False
docs: Helper function to determine if this node matches the given predicate.