docs: def _merge_includes(self):
          """
          If "include" option exists in "default.cfg",
          read the file(glob-match) in the directory.
          """
          raw_include_path = self.get_global_include()
          if raw_include_path:
              abs_include_path = self._get_global_include_abs_path(
                  raw_include_path
              )
              self._validate_global_include(abs_include_path)
              self.set_global_include(abs_include_path)
  
              for infile in glob.glob(abs_include_path):
                  self.config.merge(
                      self._configobj_factory(infile=infile)
                  )