C lang: array names and indexes can be swapped

#include <stdio.h>

int main()
{
    char a[] = {'a', 'b', 'c'};
    int b = 1;
    
    printf("--%c--\n", a[b]);
    printf("--%c--\n", b[a]);
    printf("--%c--\n", 1[a]);
    
    return 0;
}

All three print the same --b--.

Why? The direct access would be using pointer *(a + b) and there the plus sign is commutative. The bracket notation is just syntactic sugar and apparently it does not check for the weird swapped notation.