FocusTrapModal [constraint] v1.0.0

Every modal dialog must implement a focus trap: keyboard focus must be sent into the modal on open, cycle within the modal on Tab / Shift+Tab, and return to the triggering element on close.

Target

• modal dialogs
• blocking drawers
• any aria-modal=true overlay

Severity

critical

Values

• • Required: initial focus moves into the modal (first focusable element or named initial focus target)
• • Required: Tab from the last focusable element returns to the first inside the modal
• • Required: Shift+Tab from the first focusable element returns to the last inside the modal
• • Required: Escape key closes the modal (unless explicitly forbidden by the dialog semantics)
• • Required: focus restored to the triggering element on close
• • Required: aria-modal='true' and role='dialog' on the dialog container
• • Required: aria-labelledby pointing to the dialog title

Exceptions

• Non-modal dialogs (e.g., docked side panels with role='dialog' but no aria-modal) — must not trap.
• Tooltips and popovers — focus trap forbidden, follow popover semantics instead.

Approved Alternatives

• Use Radix Dialog (focus-trap-react under the hood).
• Use React Aria useDialog + useModalOverlay hooks.
• Use the native
  element with .showModal() — built-in focus trap.
• Headless UI
  for React/Vue.

Enforcement

Storybook a11y addon. Cypress test per modal: open, Tab repeatedly, assert focus stays inside; press Escape, assert focus returns to trigger.

FocusTrapModal [constraint] v1.0.0

Every modal dialog must implement a focus trap: keyboard focus must be sent into the modal on open, cycle within the modal on Tab / Shift+Tab, and return to the triggering element on close.

Target

• modal dialogs
• blocking drawers
• any aria-modal=true overlay

Severity

critical

Values

• • Required: initial focus moves into the modal (first focusable element or named initial focus target)
• • Required: Tab from the last focusable element returns to the first inside the modal
• • Required: Shift+Tab from the first focusable element returns to the last inside the modal
• • Required: Escape key closes the modal (unless explicitly forbidden by the dialog semantics)
• • Required: focus restored to the triggering element on close
• • Required: aria-modal='true' and role='dialog' on the dialog container
• • Required: aria-labelledby pointing to the dialog title

Exceptions

• Non-modal dialogs (e.g., docked side panels with role='dialog' but no aria-modal) — must not trap.
• Tooltips and popovers — focus trap forbidden, follow popover semantics instead.

Approved Alternatives

• Use Radix Dialog (focus-trap-react under the hood).
• Use React Aria useDialog + useModalOverlay hooks.
• Use the native
  element with .showModal() — built-in focus trap.
• Headless UI
  for React/Vue.

Enforcement

Storybook a11y addon. Cypress test per modal: open, Tab repeatedly, assert focus stays inside; press Escape, assert focus returns to trigger.

Rationale

Without a focus trap, Tab key escapes into the underlying page content — which is visually obscured but still focusable. Screen-reader and keyboard users get ejected to invisible controls and lose context. WCAG 2.1.2 (No Keyboard Trap) sounds contradictory but it specifically permits modal traps as long as Escape / standard close exists. Native <dialog showModal()> and Radix Dialog implement this correctly; hand-rolled overlays almost never do.