How to use the niworkflows.utils.spaces.SpatialReferences function in niworkflows

def init_spaces(checkpoint=True):
    """Initialize the :attr:`~workflow.spaces` setting."""
    from niworkflows.utils.spaces import Reference, SpatialReferences

    spaces = execution.output_spaces or SpatialReferences()
    if not isinstance(spaces, SpatialReferences):
        spaces = SpatialReferences(
            [ref for s in spaces.split(" ") for ref in Reference.from_string(s)]
        )

    if checkpoint and not spaces.is_cached():
        spaces.checkpoint()

    # Make the SpatialReferences object available
    workflow.spaces = spaces

def parse_args(args=None, namespace=None):
    """Parse args and run further checks on the command line."""
    import logging
    from niworkflows.utils.spaces import Reference, SpatialReferences

    parser = _build_parser()
    opts = parser.parse_args(args, namespace)
    config.execution.log_level = int(max(25 - 5 * opts.verbose_count, logging.DEBUG))
    config.from_dict(vars(opts))
    config.loggers.init()

    # Initialize --output-spaces if not defined
    if config.execution.output_spaces is None:
        config.execution.output_spaces = SpatialReferences([Reference("run")])

    # Retrieve logging level
    build_log = config.loggers.cli

    if config.execution.fs_license_file is None:
        raise RuntimeError(
            """\
ERROR: a valid license file is required for FreeSurfer to run. dMRIPrep looked for an existing \
license file at several paths, in this order: 1) command line argument ``--fs-license-file``; \
2) ``$FS_LICENSE`` environment variable; and 3) the ``$FREESURFER_HOME/license.txt`` path. Get it \
(for free) by registering at https://surfer.nmr.mgh.harvard.edu/registration.html"""
        )
    os.environ["FS_LICENSE"] = str(config.execution.fs_license_file)

    # Load base plugin_settings from file if --use-plugin
    if opts.use_plugin is not None:

from niworkflows.utils.spaces import SpatialReferences, Reference
from smriprep.workflows.anatomical import init_anat_preproc_wf
wf = init_anat_preproc_wf(
    bids_root='.',
    freesurfer=True,
    hires=True,
    longitudinal=False,
    t1w=['t1w.nii.gz'],
    omp_nthreads=1,
    output_dir='.',
    skull_strip_mode='force',
    skull_strip_template=Reference('OASIS30ANTs'),
    spaces=SpatialReferences(spaces=['MNI152NLin2009cAsym', 'fsaverage5']),
)

from niworkflows.utils.spaces import SpatialReferences, Reference
from smriprep.workflows.anatomical import init_anat_preproc_wf
wf = init_anat_preproc_wf(
    bids_root='.',
    freesurfer=True,
    hires=True,
    longitudinal=False,
    t1w=['t1w.nii.gz'],
    omp_nthreads=1,
    output_dir='.',
    skull_strip_mode='force',
    skull_strip_template=Reference('OASIS30ANTs'),
    spaces=SpatialReferences(spaces=['MNI152NLin2009cAsym', 'fsaverage5']),
)

anat_only=False,
    debug=False,
    force_syn=True,
    freesurfer=True,
    fs_subjects_dir=None,
    hires=True,
    ignore=[],
    layout=BIDSLayout('.'),
    longitudinal=False,
    low_mem=False,
    omp_nthreads=1,
    output_dir='.',
    run_uuid='X',
    skull_strip_fixed_seed=False,
    skull_strip_template=Reference('OASIS30ANTs'),
    spaces=SpatialReferences(
        spaces=['MNI152Lin',
                ('fsaverage', {'density': '10k'}),
                'T1w',
                'fsnative'],
        checkpoint=True),
    subject_list=['dmripreptest'],
    use_syn=True,
    work_dir='.',
)

from niworkflows.utils.spaces import SpatialReferences, Reference
from smriprep.workflows.anatomical import init_anat_preproc_wf
wf = init_anat_preproc_wf(
    bids_root='.',
    freesurfer=True,
    hires=True,
    longitudinal=False,
    t1w=['t1w.nii.gz'],
    omp_nthreads=1,
    output_dir='.',
    skull_strip_mode='force',
    skull_strip_template=Reference('OASIS30ANTs'),
    spaces=SpatialReferences(spaces=['MNI152NLin2009cAsym', 'fsaverage5']),
)

from niworkflows.utils.spaces import SpatialReferences, Reference
from smriprep.workflows.anatomical import init_anat_preproc_wf
wf = init_anat_preproc_wf(
    bids_root='.',
    freesurfer=True,
    hires=True,
    longitudinal=False,
    t1w=['t1w.nii.gz'],
    omp_nthreads=1,
    output_dir='.',
    skull_strip_mode='force',
    skull_strip_template=Reference('OASIS30ANTs'),
    spaces=SpatialReferences(spaces=['MNI152NLin2009cAsym', 'fsaverage5']),
)

def get(cls):
        """Return defined settings."""
        out = {}
        for k, v in cls.__dict__.items():
            if k.startswith("_") or v is None:
                continue
            if callable(getattr(cls, k)):
                continue
            if k in cls._paths:
                v = str(v)
            if isinstance(v, _SRs):
                v = " ".join([str(s) for s in v.references]) or None
            if isinstance(v, _Ref):
                v = str(v) or None
            out[k] = v
        return out

from niworkflows.utils.spaces import SpatialReferences, Reference
from smriprep.workflows.anatomical import init_anat_preproc_wf
wf = init_anat_preproc_wf(
    bids_root='.',
    freesurfer=True,
    hires=True,
    longitudinal=False,
    t1w=['t1w.nii.gz'],
    omp_nthreads=1,
    output_dir='.',
    skull_strip_mode='force',
    skull_strip_template=Reference('OASIS30ANTs'),
    spaces=SpatialReferences(spaces=['MNI152NLin2009cAsym', 'fsaverage5']),
)

def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest,
                SpatialReferences([Space.from_string(v) for v in values]))