amp-inabox is an AMP page living inside a x-origin iframe with scrolling disabled. So the whole iframe scrolls with the host document. The major use case is to display A4A in such an iframe in a non-AMP document.

The AMP runtime inside the iframe needs to communicate to the host doc, so that it can

• get viewport position which is essential for visibility tracking, resource scheduling and video autoplay etc.
• get host document info which is needed for amp-analytics to work
• ask for iframe resizing

A messaging channel needs to be established between the host doc and AMP in the iframe. So we propose a pair of scripts named amp-inabox.js and amp-inabox-host.js to be installed at each end.

More precisely, amp-inabox.js is compiled as a different runtime entrypoint, and served at https://cdn.ampproject.org/amp4ads-v0.js. It is to replace the v0.js runtime script in an A4A creative. amp-host-v0.js is a standalone script that will be loaded on the host doc.

Planned work:

• introduce new entry point for AMP runtime, and served as amp4ads-v0.js (delivered)
• sample bootstrap code for host page to load amp-inabox-host.js (delivered)
• update spec & validator
• viewport API

Future work:

• docinfo API
• resize API