When you create a Web Block, the following runtime property is available:
RuntimeId: Identifies the web block within the screen where it is running.
Read only. Text type.
In previous versions, the RuntimeId was used in the extended properties, to "compose" the HTML identifiers of the widgets used in the screen or block. From this version on, this is no longer necessary because all widgets have their own identifier, obtained through their id runtime property.
About Runtime Properties