To use a xor gate, you need to select the xor gate, click on constraints field in the property view. You will see a pop up like this :
https://community.jboss.org/servlet/JiveServlet/downloadImage/2-810022-20669/310-155/Untitled.png
Click on edit. You will get another pop up like below :
https://community.jboss.org/servlet/JiveServlet/downloadImage/2-810022-20670/450-337/Untitled.png
Variable is a process variable. You can set its value before the xor gate in the flow is reached.
You can set a value similarly in the other constraint as well. Which ever value is matched, it will be returned.
