Attempt to register customized DublinCore behavior

from zope import schema
from plone.directives import form
from z3c.form.interfaces import IEditForm
from z3c.form.interfaces import IAddForm
from plone.app.dexterity.behaviors.metadata import _ as _dx
from plone.autoform.interfaces import IFormFieldProvider
from zope.interface import alsoProvides
from plone.app.dexterity.behaviors import metadata


class ICustomCategorization(form.Schema):
    # categorization fieldset
    form.fieldset(
        'categorization',
        label=_dx(u'Categorization'),
        fields=['subjects', 'language'],
        )

    subjects = schema.Tuple(
        title=_dx(u'label_categories', default=u'Categories'),
        description=_dx(u'help_categories', default=u'Also known as keywords, tags or labels, these help you categorize your content.'),
        value_type=schema.TextLine(),
        required=False,
        missing_value=(),
        )
    # form.widget(subjects = TextLinesFieldWidget)

    language = schema.Choice(
        title=_dx(u'label_language', default=u'Language'),
        vocabulary='plone.app.vocabularies.AvailableContentLanguages',
        required=False,
        missing_value='',
        )

    form.omitted('subjects', 'language')
    form.no_omit(IEditForm, 'subjects', 'language')
    form.no_omit(IAddForm, 'subjects', 'language')

alsoProvides(ICustomCategorization, IFormFieldProvider)


class CustomCategorization(metadata.MetadataBase):

    def _get_subjects(self):
        return self.context.subject

    def _set_subjects(self, value):
        self.context.subject = value
    subjects = property(_get_subjects, _set_subjects)

    language = metadata.DCFieldProperty(ICustomCategorization['language'], get_name='Language', set_name='setLanguage')


class ICustomDublinCore(metadata.IOwnership, metadata.IPublication, ICustomCategorization, metadata.IBasic):
    """ Metadata behavior providing all the DC fields
    """
    pass


class CustomDublinCore(metadata.Basic, CustomCategorization, metadata.Publication, metadata.Ownership):
    pass


##### configure.zcml

    <plone:behavior
        title="Categorization"
        description="Adds keywords and language setting"
        provides=".metadata.ICustomCategorization"
        factory=".metadata.CustomCategorization"
        for="plone.dexterity.interfaces.IDexterityContent"
        />

    <plone:behavior
        title="Dublin Core metadata 2"
        description="Adds Dublin Core metadata fields (equals Basic metadata + Categorization + Effective range + Ownership)"
        provides=".metadata.ICustomDublinCore"
        factory=".metadata.CustomDublinCore"
        for="plone.dexterity.interfaces.IDexterityContent"
        />