code: def surface(self, tag):
          ''' Get surface string that is associated with a tag object '''
          if tag.cfrom is not None and tag.cto is not None and tag.cfrom >= 0 and tag.cto >= 0:
              return self.text[tag.cfrom:tag.cto]
          else:
              return 'f surface(self, tag):
          ''' Get surface string that is associated with a tag object '''
          if tag.cfrom is not None and tag.cto is not None and tag.cfrom >= 0 and tag.cto >= 0:
              return self.text[tag.cfrom:tag.cto]
          else:
              return ''
docs: Get surface string that is associated with a tag object