From OpenSCADAWiki
To add the processing logic of the "Cooler" widget, open the dialog for the properties editing of this visual element and go to the tab "Processing". In this tab we will see the attributes tree of the widget and the text field of the attributes processing program. To solve our task we need to add three attributes: Ti, To, Cw (Fig.5.3.2.14); for which you need to unroll the root element ".", select any item inside it and click the button "Add attribute" below.