Pi Zero On/Off button

[sou1f1y33]

I followed the GitHub instructions to add a on/off momentary button to my pi zero but I can only get the pi to turn on from the button. Below is what i edited in the config text and took out the semi colon for the push button switch. Any ideas what I am doing wrong? can the pi zero not do this?

;system.power.switch=PIN56ONOFF
system.power.switch=PIN56PUSH