3. How to sort blocks by priority?
Often a customer may qualify for multiple blocks of the same type within checkout. In order to determine which block a customer will be shown, the block priority is used. Block priorities are set for each block type such as Checkout Order bump and Checkout Shipping Upsell. Blocks will be sorted by priority and a customer will be shown the first block for which they are eligible for.
It's recommend to make the blocks with the most specific display rules first and more general blocks last.