Interface AnimationPhase

Animation phase. Rules (applied to both show and hide):

• Unique target property. At most one tween per (target node, property) pair in a phase. A second one is a load-time error.
• Target must exist. target must resolve to a node id in the tree at load time, otherwise the overlay fails to register.
• Empty tween is a no-op. A tween with neither explicit from nor to and whose implicit values coincide silently does nothing.
• duration: 0 is allowed. Instant snap to to at delay time; property then stays at to for the rest of the phase.
• Settle to base on phase end. When the phase finishes, every tweened property snaps to the node's declared base value from OverlayDefinition - even if the tween's explicit to was different. The base value (mutated by patch()) is the canonical resting state; to is only a trajectory target during the phase.
• Patch during phase. Calls to patch() that land while a tween is in flight do not retarget the tween - neither its explicit nor implicit to is re-resolved. The patched base takes effect at the phase-end settle (see above) and on the next phase.