In your web screens or web blocks you can define one default button or link. This behavior is implemented through the Default property of the Button widget or Link widget.
When you define a Button or Link widget as default it means that pressing the ENTER key in any one of the following widgets:
Has exactly the same effect as directly pressing the button or the link.
In each Web Screen and Web Block, you can have only one default button or link. If you specify more than one button or link as default, only the last one that is set as default is considered; the previous one is automatically disabled.
Button Properties | Link Properties