motion/validatable.rb
def error_messages_for(field)
      key = field.to_sym
      error_messages.select{|message| message.has_key?(key)}.map{|message| message[key]}
    end
def error_messages_for(field)
      key = field.to_sym
      error_messages.select{|message| message.has_key?(key)}.map{|message| message[key]}
    end
Array of messages for a given field. Results are always an array
 because a field can fail multiple validations.