allowed: boolean

function onRequestEditOperation(s, e) {
    if(e.operation === DiagramEditOperation.ResizeShape) {
        if(e.args.newSize.width < 1 || e.args.newSize.height < 0.75) {
            if(e.reason !== DiagramRequestEditOperationReason.CheckUIElementAvailability)
                showWarning("The shape size is too small.");
            e.allowed = false;
        }
    }
    else if(e.operation === DiagramEditOperation.ChangeShapeText) {
        if(e.args.text === "") {
            if(e.reason !== DiagramRequestEditOperationReason.CheckUIElementAvailability)
                showWarning("A shape text cannot be empty.");
            e.allowed = false;
        }
    }
    ...
}