'Mark field ``field_name`` of expected block usage ``usage_id`` as ignored
Args:
usage_id (:class:`opaque_keys.edx.UsageKey` or ``None``). If ``None``, skip, this field in all blocks
field_name (string): The name of the field to skip'

def exclude_field(self, usage_id, field_name):

    self.field_exclusions.add((usage_id, field_name))
