This page is intended to keep notes of “features” undocumented by Facebook.
API
Poke
There is no official way to make a poke through Graph API calls. (source)
Posts
In any status, post or chat message, if you use [[fb_unique_id]] or [[fb_username]] (between double brackets), it will get converted to the “profile” icon of that user or page id. (source)
@[fb_unique_id:0] will be converted into a link to that user profile or page. (ref)
It is not possible to post yopmail.com addresses in chat or status. Although it is possible to use yopmail known aliases.