+EinR |bool |isGCB |const GCB_enum before|const GCB_enum after
+EsR |bool |isLB |LB_enum before \
+ |LB_enum after \
+ |NN const U8 * const strbeg \
+ |NN const U8 * const curpos \
+ |NN const U8 * const strend \
+ |const bool utf8_target
+EsR |LB_enum|advance_one_LB |NN U8 ** curpos \
+ |NN const U8 * const strend \
+ |const bool utf8_target
+EsR |LB_enum|backup_one_LB |NN const U8 * const strbeg \
+ |NN U8 ** curpos \
+ |const bool utf8_target