Window rules to center floating window on another window

[omnigenous]

I know class and title of parent window that I want to center child floating window on. I couldn't figure out if this possible after reading https://wiki.hyprland.org/Configuring/Window-Rules/ but I don't fully understand move section.

So far I got:

windowrulev2 = float, class:App title:App child
windowrulev2 = size 900 500, class:App title:App child
# now center it on parent window

I know center exists but I don't want to center on monitor I want to center on specific parent window with same class.