In previous versions of Thingworx, you could put jQuery in an Expression widget and it would allow you to force focus to a specific field. This was useful for Mashups that integrate with some sort of keyboard wedge type device (barcode scanner, USB RFID reader, etc.). Additionally, this could be useful for any form/data entry screen where a user presses Done/Save and the screen can reset for the next entry.
In 8.4 and above, this functionality was lost with the new Expression Function. Currently there is no way to force focus to an user input field.
The idea here is to provide bindable Services on the user input widgets that can be called to set focus to that widget based on some other event happening on the Mashup.