Custom validation attachment points

[Shadowfiend]

Currently validation errors are always attached to the generated name of the associated field. It would be handy to allow for validations for a given field to be attached to a different identifier at a field level, and possibly also at a validation level. For example, say I have a hidden field, but I want to display its validation associated with a visible analogue to the field. In this case, I would need to do some client-side scripting to take the error attached to the hidden field and put it with the visible field. Instead, we could imagine:

  val myHiddenField = field[String](".selector").validatingAs("visible-field") ? ...