code: function cast(values, name) {
    var value = values && typeof values === 'string' ? [values] : values
  
    if (!value || typeof value !== 'object' || !('length' in value)) {
      throw new Error(
        'Invalid ' + name + ' `' + value + '`, expected non-empty string'
      )
    }
  
    return value
  }
docs: Validate tags or ranges, and cast them to arrays.