Is "cancel" a keyword or reserved word in Photoshop?

Question

Is "cancel" a keyword or reserved word?

My simple dialog box:

var dlg = new Window("dialog"); 
    dlg.text = "Proceed?"; 
    dlg.preferredSize.width = 160; 

// GROUP1
// ======
var group1 = dlg.add("group", undefined, {name: "group1"}); 
    group1.preferredSize.width = 160; 

// add buttons
var button1 = group1.add ("button", undefined);
    button1.text = "OK";
var button2 = group1.add ("button", undefined);
    button2.text = "Cancel";


var myReturn = dlg.show();

if (myReturn == 1)
{
   // code here
}

Works fine. All is well. However replace the string "Cancel" with "Can" and the button no longer functions.

You need to add extra code in order to regain functionality.

button2.onClick = function()
{
  // alert("Byas!");
  dlg.close();
  dialogResponse = "cancel";
}

So, what's going on, is "cancel" a keyword?