At #facevalue "readers" fact checked Elon's own tweet.

I don't know #Twitter well enough to know how its #SiteMechanics work to know if #ReadersContext is a common thing or not.

Unless readers = employees of Twitter, I don't know how to interpret this.

At face value some readers added some context, like on YouTube at one point some strangers could add subtitles to videos they liked.

Anyone from Twitter who knows how "Readers added context" works?