There are some Minecraft servers that have a unique feature on the player limits: They have their limit set to 1, but players can still join. Here is a picture as an example of an existing Minecraft server that has this feature:
I prefer not to show what server that is, but if it is needed, please let me know.
I was wondering: What is this unique feature?
Is it available for all servers that want it?
Will I be able to obtain it on my server, if yes, how?
I am in PC/Java (Windows) [Edited]