@view_config(renderer='templates/form.pt', name='deferred_schema_bindings')
    @demonstrate('Deferred Schema Bindings')
    def deferred_schema_bindings(self):
        import datetime
        import colander
        @colander.deferred
        def deferred_date_validator(node, kw):
            max_date = kw.get('max_date')
            if max_date is None:
                max_date = datetime.date.today()
            return colander.Range(min=datetime.date.min, max=max_date)

        @colander.deferred
        def deferred_date_description(node, kw):
            max_date = kw.get('max_date')
            if max_date is None:
                max_date = datetime.date.today()
            return 'Blog post date (no earlier than %s)' % max_date.ctime()

        @colander.deferred
        def deferred_date_missing(node, kw):
            default_date = kw.get('default_date')
            if default_date is None:
                default_date = datetime.date.today()
            return default_date

        @colander.deferred
        def deferred_body_validator(node, kw):
            max_bodylen = kw.get('max_bodylen')
            if max_bodylen is None:
                max_bodylen = 1 << 18
            return colander.Length(max=max_bodylen)

        @colander.deferred
        def deferred_body_description(node, kw):
            max_bodylen = kw.get('max_bodylen')
            if max_bodylen is None:
                max_bodylen = 1 << 18
            return 'Blog post body (no longer than %s bytes)' % max_bodylen

        @colander.deferred
        def deferred_body_widget(node, kw):
            body_type = kw.get('body_type')
            if body_type == 'richtext':
                widget = deform.widget.RichTextWidget()
            else:
                widget = deform.widget.TextAreaWidget()
            return widget

        @colander.deferred
        def deferred_category_validator(node, kw):
            categories = kw.get('categories', [])
            return colander.OneOf([ x[0] for x in categories ])

        @colander.deferred
        def deferred_category_widget(node, kw):
            categories = kw.get('categories', [])
            return deform.widget.RadioChoiceWidget(values=categories)

        class BlogPostSchema(colander.Schema):
            title = colander.SchemaNode(
                colander.String(),
                title = 'Title',
                description = 'Blog post title',
                validator = colander.Length(min=5, max=100),
                widget = deform.widget.TextInputWidget(),
                )
            date = colander.SchemaNode(
                colander.Date(),
                title = 'Date',
                missing = deferred_date_missing,
                description = deferred_date_description,
                validator = deferred_date_validator,
                widget = deform.widget.DateInputWidget(),
                )
            body = colander.SchemaNode(
                colander.String(),
                title = 'Body',
                description = deferred_body_description,
                validator = deferred_body_validator,
                widget = deferred_body_widget,
                )
            category = colander.SchemaNode(
                colander.String(),
                title = 'Category',
                description = 'Blog post category',
                validator = deferred_category_validator,
                widget = deferred_category_widget,
                )
        
        schema = BlogPostSchema().bind(
            max_date = datetime.date.max,
            max_bodylen = 5000,
            body_type = 'richtext',
            default_date = datetime.date.today(),
            categories = [('one', 'One'), ('two', 'Two')]
            )
        
        form = deform.Form(schema, buttons=('submit',))
        return self.render_form(form)