In theory voting is compulsory. In practice it is compulsory to show up and get your name marked off. What you do after that in the little booth with just your conscious and a pen is up to you. (I usually take the pen, that's all I've ever got out of politics.)

> In theory voting is compulsory. In practice it is compulsory to show up and get your name marked off.

Since we have a secret ballot, it would be unenforceable for them to say that you had to submit a valid ballot.

> What you do after that in the little booth with just your conscious and a pen is up to you. (I usually take the pen, that's all I've ever got out of politics.)

Odd, my voting place last election only had pencils. I carried a pen with me (voting with a pencil is asking for trouble).

You can do that in Australia. To be fair, they call them "invalid" votes and they group your vote with other votes that are not correctly filled in. Since we have a secret ballot and compulsory voting, abstaining from a vote can be done by submitting a blank ballot.