def add_insort_arg(parser):
    """
    Sort input by trail int.

    Applies :py:func:`taurenmd.libs.libio.sort_numbered_input`.

    Parameters
    ----------
    parser : `argparse.ArgumentParser <https://docs.python.org/3/library/argparse.html#argparse.ArgumentParser>`_
        The argument parser to add the insort argument.
    """
    parser.add_argument('-i', '--insort', help=
        'Sorts input trajectories paths according to their tail numbers, if paths are formatted as follows: my_trajectory_#.dcd, where # is a number.'
        , action='store_true')
