The software TouchGFX by Draupner Graphics is licensed per “Product Line”. How is this licensing metric defined?

Each “Product Line” creates a license need. A product line refers to products which have the same functionality and the same optical/structural GUI. Moreover, they are based on a microcontroller from the same series of microcontrollers.

Source: Product Line Definition_Draupner Graphics_TouchGFX_January 2017_as is 2017-11-02