figui3

Guides development and maintenance of the FigUI3 web components library for Figma-style plugin UIs. Applies when adding or modifying `fig-*` custom elements, updating docs/demo pages, adjusting theme tokens, improving accessibility, or debugging component behavior in `fig.js`, `components.css`, `index.html`, and `README.md`.

Guides CSS rendering and layout performance tests for component UIs. Use when checking selector cost, layout thrash, paint work, animation smoothness, CSS containment, computed styles, or visual regressions caused by CSS changes.

Guides browser-based performance testing for HTML, CSS, JavaScript, and UI interactions. Use when measuring frontend performance, adding Playwright perf tests, checking regressions, profiling load/render/interaction cost, or discussing performance budgets.

Guides JavaScript runtime performance testing for frontend components. Use when profiling event handlers, DOM update loops, memory leaks, timers, animation frames, pointer/keyboard interactions, or regressions in vanilla JS component code.

Guides performance testing for native Web Components and custom elements. Use when measuring custom element registration, upgrade cost, connected/disconnected callbacks, attributeChangedCallback churn, Shadow DOM work, slots, or fig-* component scalability.

Guides accessibility review and implementation for FigUI3 web components and playground examples. Use when the user mentions accessibility, a11y, ARIA, screen readers, keyboard navigation, focus rings, labels, roles, disabled states, contrast, dialogs, menus, or form control semantics.

Guides CSS and layout tests for FigUI3 components. Use when validating component CSS, nested selectors, tokens, interaction states, computed styles, layout boxes, or visual regressions.

Guides real-browser tests for FigUI3 custom elements. Use when adding or debugging tests for fig-* web components, attribute/property contracts, value synchronization, event payloads, disabled behavior, or custom element registration.

Guides creation and refinement of Figma-style property panel patterns ("PropKit") using FigUI3 components. Applies when building or modifying property fields in the playground app (`/propkit` route), generating consistent field prompts, composing horizontal `fig-field` rows, or tuning panel UX for controls like image, color, fill, slider, switch, dropdown, segmented control, easing, and angle.

Guides development and maintenance of the FigUI3 web components library for Figma-style plugin UIs. Applies when adding or modifying `fig-*` custom elements, updating docs/demo pages, adjusting theme tokens, improving accessibility, or debugging component behavior in `fig.js`, `components.css`, `index.html`, and `README.md`.

Terse communication mode—50-75% fewer tokens. Do work, report result, stop. No preamble, no self-narration.

Implements CSS nesting and advanced selectors with progressive enhancement and maintainable specificity. Use when writing or refactoring nested CSS, or when the user mentions :has, :is, :where, :not, or complex selector composition.