+EsnR |bool |isGCB |const PL_GCB_enum before|const PL_GCB_enum after
+EsR |PL_WB_enum|advance_one_WB|NN U8 ** curpos \
+ |NN const U8 * const strend \
+ |const bool utf8_target
+EsR |PL_WB_enum|backup_one_WB|NN PL_WB_enum * previous \
+ |NN const U8 * const strbeg \
+ |NN U8 ** curpos \
+ |const bool utf8_target
+EsR |bool |isWB |PL_WB_enum previous \
+ |PL_WB_enum before \
+ |PL_WB_enum after \
+ |NN const U8 * const strbeg \
+ |NN const U8 * const curpos \
+ |NN const U8 * const strend \
+ |const bool utf8_target