Whereas form level Validators set their msg in form.note in case they fail, field level Validators don't. That means that if you validate a form and somewhere a field validator fails, you have no clue which one.

Is this designed behavior? If not, may I suggest to change:
https://github.com/webpy/webpy/blob/master/web/form.py#L107

out = i.validate(v) and out

to:

if not i.validate(v):
    self.note = i.note
    return False

Instead of return False one could also do out = False, but actually I think it is better to fail first on a field validator than on a (typically more complex) form validator