NOTMUCH_FIELD_NO_FLAGS = 0,
NOTMUCH_FIELD_EXTERNAL = 1 << 0,
NOTMUCH_FIELD_PROBABILISTIC = 1 << 1,
NOTMUCH_FIELD_PROCESSOR = 1 << 2,
NOTMUCH_FIELD_NO_FLAGS = 0,
NOTMUCH_FIELD_EXTERNAL = 1 << 0,
NOTMUCH_FIELD_PROBABILISTIC = 1 << 1,
NOTMUCH_FIELD_PROCESSOR = 1 << 2,