I didn't understand
I do understand
pro:sub mod v
i didn't understand .
aɪ WORD_BOUNDARY d ɪ d n t WORD_BOUNDARY ʌ n d ə ɹ s t æ n d WORD_BOUNDARY
i WORD_BOUNDARY d i d n ' t WORD_BOUNDARY u n d e r s t a n d WORD_BOUNDARY