Field ??? not expected

Stack:

• Python 3.4 (using virtualenv)
• Pyramid 1.5.2
• Jinja2 (as Template Engine)
• SimpleForm (hacked for compability with Python 3)
• FormEncode

So I encounter the error which from the stack trace I almost cannot conclude anything. By debugging SimpleForm (yes, you read it correctly... debugging) finally I able to capture the real error messages which is like

field submit not expected

or

field _csrf not expected

With the real error message in hand, the quick googling deliver me to this link: https://github.com/Pylons/pyramid_simpleform/issues/6

Oh ok, seems like I need to add something to my schema

class MySchema(Schema):
    allow_extra_fields = True
    filter_extra_fields = True

    name = validators.UnicodeString(min=5)
    value = validators.Int()

Yes, it's because of allow_extra_fields and filter_extra_fields, and the curiosity of "why" lead me to this page: https://github.com/Pylons/pyramid_simpleform/blob/master/docs/index.rst
which stated:

Note the use of the allow_extra_fields and filter_extra_fields attributes. These are recommended in order to remove unneeded fields (such as the CSRF) and also to prevent extra field values being passed through.

Oh Desson, please RT*M!