code: def _check_reference(inst, ch_names=None):
      """Check for EEG ref."""
      info = inst.info
      if ch_names is not None:
          picks = [
              ci
              for ci, ch_name in enumerate(info["ch_names"])
              if ch_name in ch_names
          ]
          info = pick_info(info, sel=picks)
      if _needs_eeg_average_ref_proj(info):
          raise ValueError(
              "EEG average reference (using a projector) is mandatory for "
              "modeling, use the method set_eeg_reference(projection=True)"
          )
      if _electrode_types(info) and info.get(
          "custom_ref_applied", False
      ):
          raise ValueError(
              "Custom EEG reference is not allowed for inverse "
              "modeling."
          )
  
imports: from copy import deepcopy
  from math import sqrt
  import numpy
  from scipy import linalg
  from scipy.stats import chi2
  from .._fiff.constants import FIFF
  from .._fiff.matrix import _read_named_matrix, _transpose_named_matrix, write_named_matrix
  from .._fiff.open import fiff_open
  from .._fiff.pick import channel_type, pick_channels, pick_info, pick_types
  from .._fiff.proj import _electrode_types, _needs_eeg_average_ref_proj, _read_proj, _write_proj, make_projector
  from .._fiff.tag import find_tag
  from .._fiff.tree import dir_tree_find
  from .._fiff.write import end_block, start_and_end_file, start_block, write_coord_trans, write_float, write_float_matrix, write_int, write_string
  from ..cov import Covariance, _read_cov, _write_cov, compute_whitener, prepare_noise_cov
  from ..epochs import BaseEpochs, EpochsArray
  from ..evoked import Evoked, EvokedArray
  from ..fixes import _safe_svd
  from ..forward import _read_forward_meas_info, _select_orient_forward, compute_depth_prior, compute_orient_prior, convert_forward_solution, is_fixed_orient
  from ..forward.forward import _triage_loose, write_forward_meas_info
  from ..html_templates import _get_html_template
  from ..io import BaseRaw
  from ..source_estimate import _get_src_type, _make_stc
  from ..source_space._source_space import _get_src_nn, _get_vertno, _read_source_spaces_from_tree, _write_source_spaces_to_fid, find_source_space_hemi, label_src_vertno_sel
  from ..surface import _normal_orth
  from ..time_frequency.tfr import _check_tfr_complex
  from ..transforms import _ensure_trans, transform_surface_to
  from ..utils import _check_compensation_grade, _check_depth, _check_fname, _check_option, _check_src_normal, _validate_type, _verbose_safe_false, check_fname, logger, repr_html, verbose, warn
  from ._eloreta import _compute_eloreta
label_desc: Use image node_id 11 for calling a global function with example usage: _check_reference(inst, ch_names) without return types