docs: def split_focus(self):
          """Divide the focus edit widget at the cursor location."""
  
          focus = self.lines[self.focus]
          pos = focus.edit_pos
          edit = urwid.Edit("", focus.edit_text[pos:], allow_tab=True)
          edit.original_text = ""
          focus.set_edit_text(focus.edit_text[:pos])
          edit.set_edit_pos(0)
          self.lines.insert(self.focus + 1, edit)