Ockwell-Smith is one of the leading proponents of gentle parenting, and this short book focuses on the specific challenges of potty training. She leads off with the physiology of waste, kidneys and colon, and the development of sphincter control at about 24 months of age. Of course, physiological control doesn't mean psychological control, and learning to listening to your body and then going to the bathroom is something children have to figure out for themselves.
Some of the practical advice is good. Potty training is messy and there will be accidents, so carry spare clothes and waterproof everything. The foot supported squat is the natural excretory posture, which means little potties are probably best. Constipation is a frequently undiagnosed contributor to potty-training problems, both directly, and also because loose stools leak around the constipated mass, and the the mass presses on the bladder decreasing its effective size. Night potty training has additional challenges, as children have both uneven circadian rhythms are irregular levels of vasopressin, which suppresses urine formation in adults, and not enough experience to wake up when they do need to pee. The path is long, and there will be reversals.
The psychological advice is where I am less convinced. I'll buy that ease is a necessary condition for potty training, and that enticement and punishment are not particularly effective. Sticker charts, small treats, big presents, getting mad, none of that works. But what do you do when you ask your kid if he has to use the bathroom, he says "No thank you", and he then pees himself five minutes later?
I know patience is the acme of gentle parenting. But my patience has limits.