This is one of the factors that may limit their size.
ð ɪ s WORD_BOUNDARY ɪ z WORD_BOUNDARY w ʌ n WORD_BOUNDARY ʌ v ð ə WORD_BOUNDARY f æ k t ə ɹ z WORD_BOUNDARY ð æ t WORD_BOUNDARY m eɪ WORD_BOUNDARY l ɪ m ɪ t WORD_BOUNDARY ð ɛ ɹ WORD_BOUNDARY s aɪ z WORD_BOUNDARY