Can not use a ‘priority-rat = key_word’?

Somebody advised to me ‘priority-rat = key_word’
if bot sees a rat on overview with key_word in its name, it should kill it with higher priority.

However, the following error message was displayed.

Failed to parse these app-setting: Unknown setting name ‘priority-rat’.

I want use a ‘priority-rat = Alvi’

You can use the priority-rat setting here: FrontendWeb.Main