Stacking order
What is above and what is below

The right-click menu with the Arrange submenu open: Bring to front, Send to back, Move up, Move down

The Arrange menu

Right-click menu › Arrange:

ItemKeysWhat it does
Bring to front⌘ Fabove all its siblings
Send to back⌘ Bbelow all its siblings
Move up⌘ ⇧ Fup one level
Move down⌘ ⇧ Bdown one level

The order applies within the object's container (the page, the group). In the Document tree the rows follow the same order.