def load_common_meta(loader, filename):
    """
    Open an existing file and return any meta-data common to all data groups
    (eg. a FITS primary header) as a dict-like (eg. PyFITS header) object.

    Parameters
    ----------

    filename : `str`
        Name of an existing file from which to get the meta-data common to all
        groups of pixel data within that file.

    Returns
    -------

    `dict`-like
        A meta-data dictionary or compatible object.

    """
    return loader(filename)