docs: def _available_channels(devices, header):
      """
      Function used for the determination of the available channels in each device.
  
      ----------
      Parameters
      ----------
      devices : list ["mac_address_1" <str>, "mac_address_2" <str>...]
          List of devices selected by the user.
  
      header: dict
          Dictionary that contains auxiliary data of the acquisition.
  
      Returns
      -------
      out : dict
          Returns a dictionary where each device defines a key and the respective value will be a list
          of the available channels for the device.
  
      """
  
      # ------------------------ Definition of constants and variables ------------------------------
      chn_dict = {}
  
      # %%%%%%%%%%%%%%%%%%%%%% Access to the relevant data in the header %%%%%%%%%%%%%%%%%%%%%%%%%%%%
      for dev in devices:
          chn_dict[dev] = header[dev]["column labels"].keys()
  
      return chn_dict