To reproduce, look at the command syntax help for /clear
:
Type in
/clear
Hit the space bar
Hit
esc
You will see the command syntax help for /clear:
/clear [<targets>] [<item>]
(see attached screenshot)
The provided syntax suggests that
/clear minecraft:enchanted_book{}
is valid, which it isn't.
The correct syntax help for this example should be /clear [<targets> [<item>]]
.
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I do not believe that, but people unfamiliar with Minecraft's command system might when seeing this syntax help.
It only suggests that if you believe that optionals can be left out no matter their position, which is not true. An optional is required if you want to specify more arguments after it.