code: def read_raw_snirf(
      fname, optode_frame="unknown", preload=False, verbose=None
  ) -> "RawSNIRF":
      """Reader for a continuous wave SNIRF data.
  
      .. note:: This reader supports the .snirf file type only,
                not the .jnirs version.
                Files with either 3D or 2D locations can be read.
                However, we strongly recommend using 3D positions.
                If 2D positions are used the behaviour of MNE functions
                can not be guaranteed.
  
      Parameters
      ----------
      fname : path-like
          Path to the SNIRF data file.
      optode_frame : str
          Coordinate frame used for the optode positions. The default is unknown,
          in which case the positions are not modified. If a known coordinate
          frame is provided (head, meg, mri), then the positions are transformed
          in to the Neuromag head coordinate frame (head).
      %(preload)s
      %(verbose)s
  
      Returns
      -------
      raw : instance of RawSNIRF
          A Raw object containing fNIRS data.
          See :class:`mne.io.Raw` for documentation of attributes and methods.
  
      See Also
      --------
      mne.io.Raw : Documentation of attributes and methods of RawSNIRF.
      """
      return RawSNIRF(fname, optode_frame, preload, verbose)
  
imports: import datetime
  import re
  import numpy
  from ..._fiff._digitization import _make_dig_points
  from ..._fiff.constants import FIFF
  from ..._fiff.meas_info import _format_dig_points, create_info
  from ..._fiff.utils import _mult_cal_one
  from ..._freesurfer import get_mni_fiducials
  from ...annotations import Annotations
  from ...transforms import _frame_to_str, apply_trans
  from ...utils import _check_fname, _import_h5py, fill_doc, logger, verbose, warn
  from ..base import BaseRaw
  from ..nirx.nirx import _convert_fnirs_to_head
label_desc: Use image node_id 1 for calling a global function with example usage: read_raw_snirf(fname, optode_frame, preload, verbose) and returns: RawSNIRF