Boss bar is shown to
Whether a boss bar is currently shown to a particular player.
A Minecraft element (a check) in Scoreboards & teams. Needs the Basic plan or higher to go live; building and testing are free.
Example
When a player uses a command → If Boss bar is shown to arena → Answer: You can see it.
Also called
sees bar, bar shown, viewing bar
Works as a data pack?
No. This one needs the Elementium plugin on a Paper server.
What you give it
- Bar
- Player