'Return server side errors. Shall be overridden by derived forms to add their
extra errors for AngularJS.'

def get_field_errors(self, field):

    identifier = format_html(u'{0}.{1}', self.form_name, field.name)
    errors = self.errors.get(field.html_name, [])
    return self.error_class([SafeTuple((identifier, self.field_error_css_classes, u'$pristine', u'$pristine', u'invalid', e)) for e in errors])
