Live command argument descriptors [NOT AUTOCOMPLETE]

While returning a live list of possible command auto-complete arguments is well documented, I havent seen anyone talk about this topic:
In some cases, you want to get a unique string from the player, and you cant send autocomplete values. It can be helpful to indicate what their inputted string should mean.
Minecraft does this. With the scoreboard command, when defining your own objective name, the game shows you a greyed out bracketed map of what the rest of the command should look like:
<objective> <criteria> [<displayName>]
Here is a screenshot! Try it out for yourself!

Is is server-side or client? How do I do it with my commands? Do I just return a size()=1 list with arguments with brackets? WHAT IS THIS WITCHCRAFT AND WHY IS NO-ONE TALKING ABOUT IT!!?!??!?!?!
MeechaPooch

 

I just put it in for the autocomplete in my plugins, sure if they click tab it will pop it in but most people are smart enough to think that if it says '<number>' it actually wants a number input.