Virtual Wire & Virtual System assignment issue

[T.Zidane]

Hi,
I hope this message finds you all well 🙂

I have some configurations questions regarding virtual wire in PAN-OS FW that support multiple virtual systems, i would like to get some official documents regarding virtual wire configuration and assign it to vsys part,
In Network tab > Virtual Wires, there are the following columns : Name, Interface1, Interface2 .... Virtual System, and my questions are about "Virtual System" column, 
(1) Once creating vw and selecting the 2 interfaces from Network tab > Virtual Wires, is it mandatory to change the value "none" to vsys ID in terms of the WebUI, configurations etc ?... looks like there is some missing UI validation where it remains with "none" and not the relevant vsys ID and still working....is documented/known bug ?
(2) I can not find any documentations/guides about "Virtual System" column under tab Network > Virtual Wires, can you please provide me such docs/guides... or maybe it's something that needs to be fixed in the your recent docs/guides 
(3) In general, as part of the configuring the virtual wire, do you indicate that we should set the virtual system under this tab, if so please send me docs/guide etc.


Thanks in advance