Loads file given filename

        Args:
            filename:
            index: tab index to load file into. If not passed, loads into current tab

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)