Ownership
Components own transitions in shared source; products never re-choreograph them.
UI standard
Motion
The normative spatial and interruptible behavior for every transition.
Normative guideline
Motion
Origin
Appear, expand, and morph transitions accept the triggering action’s origin so cause and effect remain spatially continuous.
Springs
All transitions are springs and fixed-duration keyframes are outside the system, because spring motion behaves like matter (design).
Interruption
Every transition is interruptible and retargets from current position and velocity when interrupted, canceled, or reversed, because motion that cannot yield to input makes the interface lie about being ready.
First frame
Motion advances on the first frame after the input that caused it; an opening frame spent at rest reads as the product hesitating, not as ease.
Arrival
Opening answers the reader at least as briskly as dismissal, because a surface slower to arrive than to leave reads as reluctance.
Compositing
A surface that dims what is behind it paints the dim on its own scrim and never lowers the opacity of the content, so a moving surface composites one layer instead of re-rasterizing the page beneath it.
Layer promotion
Layer promotion is armed for the duration of a motion and released at rest.