class _TagParser(object):
   def __init__(self, lines):
      self._close_tag = None
      self._open_tag = None
      self._target_open_tag = None
      self._target_close_tag = None
      self._input = lines
      self.output = [ ]

   def process(self):
      pass

   def _parse(self):
      pass

   def _verifyTag(self):
      '''Check for nested or incomplete tags.'''
      in_block = False
      error = SyntaxError('Mismatching %s %s tags found.' % \
         (self._open_tag, self._close_tag))
      for line in self._input:
         if in_block:
            if self._open_tag in line:
               raise error
            elif self._close_tag in line:
               in_block = False
         else:
            if self._open_tag in line:
               in_block = True
            elif self._close_tag in line:
               raise error

