A complete spring physics solver implementing underdamped, critically damped, and overdamped systems. It calculates natural frequency (w0), damping ratio (zeta), and damped frequency (wd) to solve the spring differential equation. The class supports bidirectional conversion between physical parameters (mass/stiffness/damping) and perceptual parameters (bounce/duration), including an implementation of Apple's SwiftUI perceived duration algorithm. The solve() method uses exponential forms to prevent infinity issues. This is a self-contained, reusable physics simulation that could be extracted for any animation system needing spring dynamics.

A generic adapter registry system that extends animate() and utils.set() to work with arbitrary object types. It provides registerAdapter() for creating adapter instances, registerTargetAdapter() for per-class detection, and registerPropertyResolver() for runtime property pattern matching. The resolution order (target adapters first, then property resolvers, then direct property path) is clean and predictable. This is a well-designed plugin architecture that decouples the core engine from domain-specific targets, making it easy to add support for three.js, Babylon.js, or any other object model.

A base Clock class that manages time state, framerate, and playback rate. It provides requestTick() with a tolerance-based frame-skipping algorithm that prevents dropping frames arriving slightly early due to RAF jitter (capped at 4ms). The computeDeltaTime() method tracks elapsed time for frame-rate-independent animations. This is a clean, reusable time-management primitive that could be extracted for any animation or game loop needing consistent time stepping.

A stagger utility that generates per-target values based on position in a grid or along an axis. It supports 'from' directives (first, center, last, random, or explicit index), grid-based distribution with axis selection, easing of the stagger progression, jitter with seeded randomness, and custom 'use' functions for value mapping. The implementation is flexible and composable, accepting target/index/arrays for context-aware distribution. This is a reusable pattern for any system needing staggered or distributed value generation across a collection.

An SVG path/polygon/polyline morphing function that generates interpolated point strings between two shapes. It uses getTotalLength() and getPointAtLength() to sample equidistant points from both paths, handling different point counts by taking the maximum. The precision parameter controls sampling density. Returns a function value compatible with the animation system. This is a self-contained, reusable SVG morphing solution that could be extracted for any project needing shape tweening.

An additive animation system that blends multiple tweens targeting the same property. It maintains a lookup map of property-specific tween chains and accumulates numeric or array-based additive values before rendering. The update() method iterates all additive lookups, sums the tween values, and writes the result to the lookup tween's _toNumber/_toNumbers. This is a sophisticated composition pattern for animation layering that could be reused in any tweening system needing blend modes.

A collection of math utilities including a frame-rate-independent damping function based on Rory Driscoll's exponential decay formula. The damp() function uses lerp with an exponential factor to achieve smooth, frame-rate-independent interpolation. Also includes wrap(), mapRange(), degToRad/radToDeg, and rounding/padding helpers. The damping implementation is particularly reusable for any system needing smooth value convergence.

A timeline position parser that converts flexible position specifications into absolute millisecond offsets. It handles absolute numbers, relative operators (+=, -=, *=), sibling references (<, <<), and label lookups. The implementation cleanly separates concerns: getPrevChildOffset() handles sibling-relative parsing, while parseTimelinePosition() orchestrates the full resolution. This is a reusable pattern for any timeline or sequencing system needing expressive position syntax.