Applescript and setting checkbox variable

I'm incredibly new to coding and the like, and I've started with applescript as it is relatively easy to learn. I'm building a simple gui tool with the help of Pashua and some sample code.

I have added following code for a checkbox:

urgent.type = checkbox
urgent.lable = Urgent
urgent.default =

I tested it with a simple if then return statement:

if urgent is 1 then
   return "This is urgent!"
end if

But I'm told that the variable urgentis undefined.

I know I am missing something, but I am not sure what to do, and I've looked to no avail.

Thank you