The 'cat lean' is a feline sign that your cat likes what you do
I'll be brief. You may have seen it yourself. You should have seen it yourself! You are emotionally close to your cat. She likes it when you stroke her on the side of her body - her shoulder and flank. She likes it so much that she (a) tells you she likes it and (b) encourages you to do it. She does this by leaning towards your hand when you bring it up to her body. It becomes a natural reaction to your action. You can see it very obviously in the video below from Twitter. I call it the 'cat lean'.
I think that it is a quite important example of domestic cat body language because it is a clear signal that your cat likes what you doing. Your cat is communicating with you and, in addition both making a request and giving you feedback on the standard of your petting. Well done. You have done it right.
It is nice to get a 9/10 for petting technique. If you have seen this in your cat please share in a comment. Thanks.