How does 'assist the main assist' function work?

[Shutyergob]

How does 'assist the main assist' function work? And does it work in RoR?

I assume you just click on the 'assist the main assist' button on your UI and it then shows the target that the main assist has currently selected. Do you need to just do this once, and it stays 'in effect' for... how long? Until the main assist dies? Or is there some other amount of time?

Also, does the command /assist name work at all? And does it work the same way as the 'assist the main assist' button does? Same questions about how long it lasts applies here. How long does it last/ how often do you need to reapply it?

Please advise.

Thanks.

[GodlessCrom]

you can make a macro that is just /assist. Will assist off your defensive target. Alternatively, can use swiftassist addon though it isnt significantly more convenient imo