code: def _create_eeg_el(ch, t=None):
      """Create an electrode definition, transform coords if necessary."""
      if ch["kind"] != FIFF.FIFFV_EEG_CH:
          raise RuntimeError(
              "%s is not an EEG channel. Cannot create an "
              "electrode definition." % ch["ch_name"]
          )
      if t is None:
          t = Transform("head", "head")  # identity, no change
      if t.from_str != "head":
          raise RuntimeError("Inappropriate coordinate transformation")
  
      r0ex = _loc_to_eeg_loc(ch["loc"])
      if r0ex.shape[1] == 1:  # no reference
          w = np.array([1.0])
      else:  # has reference
          w = np.array([1.0, -1.0])
  
      # Optional coordinate transformation
      r0ex = apply_trans(t["trans"], r0ex.T)
  
      # The electrode location
      cosmag = r0ex.copy()
      _normalize_vectors(cosmag)
      res = dict(
          chname=ch["ch_name"],
          coil_class=FWD.COILC_EEG,
          w=w,
          accuracy=_accuracy_dict["normal"],
          type=ch["coil_type"],
          coord_frame=t["to"],
          rmag=r0ex,
          cosmag=cosmag,
      )
      return res
  
imports: import os
  import os.path
  from contextlib import contextmanager
  from copy import deepcopy
  from pathlib import Path
  import numpy
  from .._fiff.compensator import get_current_comp, make_compensator
  from .._fiff.constants import FIFF, FWD
  from .._fiff.meas_info import Info, read_info
  from .._fiff.pick import _has_kit_refs, pick_info, pick_types
  from .._fiff.tag import _loc_to_coil_trans, _loc_to_eeg_loc
  from ..bem import ConductorModel, _bem_find_surface, read_bem_solution
  from ..source_estimate import VolSourceEstimate
  from ..source_space._source_space import _complete_vol_src, _ensure_src, _filter_source_spaces, _make_discrete_source_space
  from ..surface import _CheckInside, _normalize_vectors
  from ..transforms import Transform, _coord_frame_name, _ensure_trans, _get_trans, _print_coord_trans, apply_trans, invert_transform, transform_surface_to
  from ..utils import _check_fname, _pl, _validate_type, logger, verbose, warn
  from ._compute_forward import _compute_forwards
  from .forward import _FWD_ORDER, Forward, _merge_fwds, convert_forward_solution
label_desc: Use image node_id 4 for calling a global function with example usage: _create_eeg_el(ch, t) and returns: res