return {
  summary = 'Get the volume of the Source.',
  description = 'Returns the current volume factor for the Source.',
  arguments = {
    {
      name = 'units',
      type = 'VolumeUnit',
      default = [['linear']],
      description = 'The units to return (linear or db).'
    }
  },
  returns = {
    {
      name = 'volume',
      type = 'number',
      description = 'The volume of the Source.'
    }
  }
}