Frames with focusable content must not have tabindex=-1

tabindex="-1" cannot be present in <frame> and <iframe> elements with focusable content.

The browser is unable to move the focus to the content included in a frame when it has a negative tabindex. This stops keyboard navigation from skipping all of its content, and if the frame is scrollable, it also prevents the focus from moving to any element from which the frame may be scrolled.

What this Accessibility Rule Checks

Examine all frame and iframe elements that contain a negative tabindex value, such as tabindex="-1". If there are any such frames, make sure they don’t have nested frames that do contain focusable items.

Learn more:

Deque Reference

Deque University - How To Fix

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