"I read with interest the suggestions of which part of the body moves first. Even Alex forgot to mention It is the knee."
Probably because in the specific situation he was describing, it IS NOT the knee.
Moore describes the action of a walk taken without rise and fall, and we can logically conclude at an altitude just below ordinary standing height. At this height, there is comparively little knee action, just a bit of flex as the leg passes under the body. As a result, his recommendation to feel the body move before the foot is quite accurate.
However, if you lower substantially, the situation changes as your knees will be far more bent. Now your knee will noticeable go first, though it must of course carry your body with it. Thus the knee moves your body across your foot and soon projects your body weight beyond your foot - with no meaningful quantity of body weight yet on the moving foot.
This action does take some time to learn. A lot of students mistkanely try to hold their hips back as their knee bends forward, so that the weight of their posterior will keep them balanced over their standing foot. This of course makes it impossible not to create a large gap in the partnership. To dance with a partner, they must learn to project the entire body, commiting their weight beyond balance into the step, so that there will be a nice vertical alignment of the standing shoulder over the standing hip over the standing knee - all advancing until they are well forwards of the standing toe. Learning to drive and commit this way, without doing it too early or too heavily is tricky, but one cannot really be said to dance until it is working.