def _structure_summary(structure):
    """
    Extract messages from the structure.
    Args:
        structure: a Pymatgen Structure object
    Returns:
        dict of the following messages:
        nsites (int): number of sites in the structure.
        is_ordered (bool): whether the structure is ordered or not.
        ...to be continued

    """
    return {"n_sites": len(structure.sites),
            "is_ordered": structure.is_ordered}