Books on Lightning

[stonelazy]

Am interested in learning and understanding Pytorch Lightning in depth. Are there any books that keep this as a focus ?
I don't need 101 lessons on Deep learning. All that am interested in knowing is the PTL as a framework.. that helps understand the answers for the questions such as what are all the knobs there to make your training quicker, explain the statement such as put self.log('val_loss',on_epoch=True), how does PTL handle combining metrics from different machines in ddp mode.. how do you transfer custom data to gpu and so on.
In a nut shell, expecting for a resource that combines lightning docs and lightning source code and presents it.