Summary

In order to have full control over accessing an iframe via keyboard use, it should be possible to set the tabindex attribute in amp-iframe.

Motivation

When I tried to make the amp.dev home page more accessible by keyboard, I found out that the user gets stuck inside the code-preview of the "AMPHTML Playground" section, which is implemented as an iframe.

Giving the amp-iframe element a tabindex="-1" to disable focusing didn't work, because the attribute won't be applied to the actual iframe element inside amp-iframe.

The biggest problem is that the user can't get out of the code-preview by using tabs, because the tab-key is mapped for indention in the code-editor. The only exception is with option/alt + tab.

Additional context

For me, it's important to implement this feature, because otherwise the developer is limited in using basic html functionality.

/cc @ampproject/wg-approvers