This nice trick extends into:
block 1
block 3;
and removing the first slash gives inverted alternation:
block 2;
block 4;
This enables you to alternate between odd and even sequential blocks :). It will extend to infinite count of blocks! Even more curious but sometimes usefull nonetheless, alternation can be switched wherever you like:
block 2;
block 4;
block 6;
can be switched into:
block 2;
block 4;
block 5;
:D ILa