code: def link(self, content, raw_url, title=''):
          
          if self.check_url(raw_url):
              url = self.rewrite_url(raw_url)
              maybe_title = ' title="%s"' % escape_html(title) if title else ''
              url = escape_html(url)
              return ('<a href="%s"%s>' % (url, maybe_title))  + content + '</a>'
          else:
              return escape_html("[%s](%s)" % (content, raw_url))
docs: Filters links.