This is a test, sorry.

    X: 1
    K: perc stafflines=1
    L:1/4
    B2 B2|B z B z|B1/2 z1/2 z B1/2 z1/2 z|B1/4 z3/4 z B1/4 z3/4 z|]


A following test:

    X: 1
    L:1/8
    K: perc stafflines=1
    z B z B|z B z B|]

And another:

    X: 1
    L:1/8
    K: perc stafflines=1
    B B - B B ||-B B2 B-|]

Final one:

    X: 1
    L:1/8
    K: perc stafflines=1
    B z B z|B z B z|]

Still trying to understand what's wrong with the above (see the [related post](https://music.stackexchange.com/a/132607/74331)).

EDIT:  
Ok, it seems like the initial `X: 1` is always required.

Still, it would really help if ABCjs would work within the editor preview too. Note that editing a previous post may give inconsistent result, and page refresh seems to be always required for some reason.