TAILQ_END
(TAILQ_FIRST(head) == TAILQ_END(head))
(var) != TAILQ_END(head); \
(var) != TAILQ_END(head) && \
(var) != TAILQ_END(head); \
(var) != TAILQ_END(head) && \
if (por2 == TAILQ_END(&block->sb_rules))
if (TAILQ_NEXT((elm2), field) != TAILQ_END(head)) \