public TabCompleter at(int position, CompletionSupplier supplier) {
        Preconditions.checkState(position < this.from);
        this.suppliers.put(position, supplier);
        return this;
    }
Marks that the given completion supplier should be used to compute tab
completions at the given index.

@param position the position
@param supplier the supplier
@return this
common/src/main/java/me/lucko/luckperms/common/command/tabcomplete/TabCompleter.java