docs: def _extract_links_from_text(self, text):
          """
          Extract supplement links from the html text. Links may be provided
          in two ways:
              1. <a> tags with href attribute
              2. <asset> tags with id attribute (requires additional request
                 to get the direct URL to the asset file)
  
          @param text: HTML text.
          @type text: str
  
          @return: Dictionary with supplement links grouped by extension.
          @rtype: {
              '<extension1>': [
                  ('<link1>', '<title1>'),
                  ('<link2>', '<title2')
              ],
              'extension2': [
                  ('<link3>', '<title3>'),
                  ('<link4>', '<title4>')
              ],
              ...
          }
          """
          supplement_links = self._extract_links_from_a_tags_in_text(text)
  
          extend_supplement_links(
              supplement_links,
              self._extract_links_from_asset_tags_in_text(text))
  
          return supplement_links