a b c book 呀
a b c book aa3
n:let n:let n:let n co
a b c book 呀 .
 WORD_BOUNDARY  WORD_BOUNDARY  WORD_BOUNDARY  WORD_BOUNDARY a˧ WORD_BOUNDARY
a WORD_BOUNDARY b WORD_BOUNDARY c WORD_BOUNDARY b o o k WORD_BOUNDARY 呀 WORD_BOUNDARY . WORD_BOUNDARY