Summary

Microsoft has announced a final date for IE11 support: https://blogs.windows.com/windowsexperience/2021/05/19/the-future-of-internet-explorer-on-windows-10-is-in-microsoft-edge/

I'd like to propose we deprecate IE11 support on an aggressive schedule to coincide with the official timings from Microsoft.

Motivation

The AMP codebase contains a significant number of workarounds for compatibility with IE11, removing these workarounds nets a smaller and more performant library (as evidenced by our module/nomodule support today).

Dropping IE11 compatibility will allow the codebase to take advantage of more modern APIs in the CSS layer and JS layer without introducing additional testing pressure to ensure polyfills work for an increasingly out of date browser platform.

Additionally, there is a significant improvement to CI by removing IE11 support (estimated to be 18m+ per execution).

Impact on Existing Users

Existing users sometimes rely on AMP to handle IE11 compatibility issues, ensuring documents render as expected (minus custom CSS). This plan removes support, and as a result could introduce broken behaviour for IE11 users.

Alternative Implementation

Alternatively, we could continue to support IE11 in the nomodule codebase and exclude CSS rules that break rendering in IE11 or are unsupported.

Additional Context

1. This falls under the "Changes that affect fewer than 0.1% of crawler-accessible AMP pages" rule. Meaning no major revision bumps are required.
2. This has now passed the two week conversation timeline per rule "Allow at least 2 weeks of open discussion after the I2D is created before proceeding with the deprecation of the feature".
3. Discussion is now planned for the June 9th Design Review.
4. Pending approval from 3 approvers, this change will be announced on the mailing list and on Slack.
5. Following announcement the change will land in roughly 6 weeks to production.

Notifications

/cc @ampproject/wg-approvers