Issue

Arising from T342395, Codex should follow the best approach or making Dialog keyboard and screenreader accessible. Premises:

• When the dialog is first opened, the focus is set in a place that makes it easy to access the content in the rest of the dialog, and it's impossible to navigate elements behind the dialog.
• The dialog is closable via keyboard

Developer notes

ARIA roles and attributes

• While aria-modal="true" removes requirement of putting aria-hidden on background content, as the aria-modal informs assistive technologies that content outside a dialog is inert, it's the safer way currently to have both attributes in use on the dialog and the background content elements.

This is most simple when teleported dialogs are the way to go, see related discussion at T343476

Keyboard navigation

• The escaping of dialogs by pressing ⎋ (ESC) has already been part since the original Dialog implementation.

Focus management

• Putting the dialog element at end of body so it is not (mistakenly) a descendant of any element that has aria-hidden set to true. See also conversation in T343476#9078810 following.

Resources

ARIA authoring practices on modal dialog and specifically on focus trapping
More on focus management:
https://allyjs.io/tutorials/accessible-dialog.html#reacting-to-kbdtabkbd-and-kbdshift-tabkbd
https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/dialog_role#focus_management

Acceptance Criteria

• Add aria-modal="true" to the already implemented role="dialog" element.
• Focus on initial dialog open should work in a predictable way.
• Users should not be able to interact with content behind the dialog when open.
  • Keep focus trap as initially implemented
  • Rely on aria-hidden="true" thank to its wider support over only aria-modal on background elements for all direct body children incl script tags
  • Add inert as future-facing attribute for non-interactable background elements
• The user should always have a way to exit the dialog using keyboard navigation. Established in initial implementation