It's currently built into the applications, not configurable by default. It's preferable if everybody in a thread / space / community uses the same one because otherwise differences can cause validation failures and conflict and thus break threads, resulting in that people can't follow many discussions, thus applications don't really expose it.
It's the kind of thing where it's preferable that either everybody switch at once, or that new applications with different "lexicon" (post types / social media format) picks a new default from the start.
It's the kind of thing where it's preferable that either everybody switch at once, or that new applications with different "lexicon" (post types / social media format) picks a new default from the start.