It was implemented by GitHub: https://blog.github.com/changelog/2018-08-17-collapse-all-diffs-in-a-pull-request-at-once/
// @vinkla
Wouldn't removing this also require the file to be renamed back to expand-collapse-outdated-comments.js?
Oh wow they matched Refined GitHub's behavior (with alt)
Hello @sindresorhus, it seems like removing this has also removed the ability to toggle/collapse all "outdated" comments in a PR page.

I no longer seem to have the functionality that was implemented in https://github.com/sindresorhus/refined-github/pull/821.
The main README says this feature was implemented by papercuts, but I am not reading anything about it.

This GH release note does not mention anything about outdated comments: https://blog.github.com/changelog/2018-08-17-collapse-all-diffs-in-a-pull-request-at-once/
And this GH release note says outdated comments will no longer auto-collapse: https://blog.github.com/changelog/2018-10-30-outdated-comments/
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Oh wow they matched Refined GitHub's behavior (with alt)