Step forward and backward in animation with "vi" movement.

[timothystone]

Compare and contrast using , and . and the use of "vi-like" movement: h,j,k,l?

H (left), back
L (right), forward

And up/down can map logically to moving in animation from the "top to the bottom of the stack."

J (down), forward
K (up), back

vi-like movement has an immediate connection to many users, even supported in emacs, and is a natural fit. While I see that , and . map to the common QWERTY keys < / , and > / . where < and > have a visual cue of "back and forward" (left and right), I think the vi-like movement has an immediate engineer/architect connection.