class ActiveModel::Error

def message

# => "is too short (minimum is 5 characters)"
error.message
error = ActiveModel::Error.new(person, :name, :too_short, count: 5)

Returns the error message. 
def message
  case raw_type
  when Symbol
    self.class.generate_message(attribute, raw_type, @base, options.except(*CALLBACKS_OPTIONS))
  else
    raw_type
  end
end