is_cancel = true-false; 

Specifies whether the button is selected when the user presses the ESC key. Possible values are true or false (default: false).

If the action expression for buttons with the is_cancel attribute set to true does not exit the dialog box (does not call done_dialog), the dialog box is automatically terminated after the action expression has been carried out, and the DIASTAT system variable is set to 0.

Only one button in a dialog box can have the is_cancel attribute set to true.