@mat talk of purity can only make all other platforms connect better among themselves. Yet every time someone implements Activity Pub the first burden they find is "ooops, this gives an error from Mastodon side".
Standards exist for this very reason.
I agree with you with meeting in the middle, but Msatodon has been up since 2016, Activity Pub since 2018, we're on 2026. Mastodon migrated in late 2017 early 2018 before the spec was even fully ratified. It's been more than 8 years.
If at-the-very-least it didn't have the "huge undocumented behaviours", it wouldn't be stalling all other AP implementers.
@benpate