Is observing the start-middle-end of breath a correct practice in Anapanasati meditation?

I was reading through Patisambhidamagga, KN . From page 164, it describes about **'Eighteen kinds of knowledge of imperfections'** related to Anapanasati(*Mahavagga->Anapanasatikatha*). Following is the except: > 1)When he goes in with mindfulness after the beginning, middle and end of the in-breath, his cognizance being distracted internally, both his body and his cognizance are disquieted, perturbed and excited. > >2)When he goes out with mindfulness after the beginning, middle and end of the out-breath, his cognizance being distracted internally, both his body and his cognizance are disquieted, perturbed and excited. > >3)With such behavior of craving as hope for, and attachment to, in-breath both his body and his cognizance are disquieted, perturbed and excited. > >4)With such behavior of craving as hope for, and attachment to, out-breath both his body and his cognizance are disquieted, perturbed and excited. > >5)Owing to longing for out-breath in him when he is fatigued by [too long or too short] in-breath is body.. > >.... Does anybody have a reference to pali canon(not commentary) where it supports the observation of start-middle-end of breath?