>>> from fivalid import validators
>>> num = validators.Number(max=20)
>>> num(10)
>>> num(21)
fivalid.validators.InvalidValueError: over max

>>> from fivalid import BaseField, validators, converters
>>> class PercentageField(BaseField):
...   validator = validators.All(
...     validators.Number(min=0, max=100),
...     validators.String())
...   converter = converters.int_converter
>>> field = PercentageField()
>>> field('99')
99
>>> field('200')
fivalid.validators.InvalidValueError: over max

>>> from fivalid import StructuredFields, Dict, BaseField
>>> from fivalid.validators import String, Length, All, Flag
>>> from fivalid.converters import truthvalue_converter
>>> class CommentField(BaseField):
...   validator = All(String(), Length(max=500))
>>> class NicknameField(BaseField):
...   validator = All(String(), Length(max=20))
>>> class RememberMeField(BaseField):
...   validator = Flag()
...   converter = truthvalue_converter
>>> rule = Dict(
...   {'comment': CommentField(required=True),
...    'nickname': NicknameField(),
...    'remember me': RememberMeField()}
... )
>>> stfields = StructuredFields(rule)
>>> stfields({'comment': 'Hello, fivalid.',
...           'nickname': 'John Doe',
...           'remember me': '1'}
... )
{'comment': u'Hello, fivalid.', 'nickname': u'John Doe', 'remember me': True}