docs: def load_filename(self, filename, index=None):
          """
          Loads file given filename
  
          Args:
              filename:
              index: tab index to load file into. If not passed, loads into current tab
          """
          filename = str(filename)  # QString protection
          if index is None:
              index = self._get_tab_index()
          page = self.pages[index]
  
          # Maybe this is set on purpose before loading attempt to leave new load_dir set (?)
          self.load_dir, _ = os.path.split(filename)
  
          clss = page.clss_load
          if len(clss) == 1:
              # If there is only one class to handle the file, will load it in a way that eventual
              # load errors will raise
              f = clss[0]()
              f.load(filename)
          else:
              # At the moment, the multi-class alternative will not display particular error information
              # if the file does not load
              f = f311.load_with_classes(filename, page.clss_load)
              if f is None:
                  raise RuntimeError("Could not load '{0!s}'".format(filename))
  
          self.load(f, index)