docs: def _operation_speak_as_spell_out(self, content, index, children):
          """
          The operation method of _speak_as method for spell-out.
  
          :param content: The text content of element.
          :type content: str
          :param index: The index of pattern in text content of element.
          :type index: int
          :param children: The children of element.
          :type children: list(hatemile.util.html.htmldomelement.HTMLDOMElement)
          """
  
          children.append(self._create_content_element(
              content[0:(index + 1)],
              'spell-out'
          ))
  
          children.append(self._create_aural_content_element(' ', 'spell-out'))
  
          return children