code: def index_content(self) -> str:
          
          # Build the toctree command
          index_filename = self.index_filename
          spacer = "    "
          toctree_lines = [
              "..  toctree::",
              spacer + ":maxdepth: {}".format(self.toctree_maxdepth),
              ""
          ]
          for f in self.files_to_index:
              if isinstance(f, FileToAutodocument):
                  rst_filename = spacer + f.rst_filename_rel_autodoc_index(
                      index_filename)
              elif isinstance(f, AutodocIndex):
                  rst_filename = (
                      spacer + f.index_filename_rel_other_index(index_filename)
                  )
              else:
                  fail("Unknown thing in files_to_index: {!r}".format(f))
                  rst_filename = ""  # won't get here; for the type checker
              toctree_lines.append(rst_filename)
          toctree = "\n".join(toctree_lines)
  
          # Create the whole file
          content = """
  .. {filename}
  
  {AUTOGENERATED_COMMENT}
  
  {prefix}
  
  {underlined_title}
  
  {introductory_rst}
  
  {toctree}
  
  {suffix}
                  """.format(
              filename=self.index_filename_rel_project_root,
              AUTOGENERATED_COMMENT=AUTOGENERATED_COMMENT,
              prefix=self.rst_prefix,
              underlined_title=rst_underline(
                  self.title, underline_char=self.index_heading_underline_char),
              introductory_rst=self.introductory_rst,
              toctree=toctree,
              suffix=self.rst_suffix,
          ).strip() + "\n"
          return content
docs: Returns the contents of the index RST file.