How to use XLSForm advanced features, like body::jr:noAddRemove

can the community provide some (useful) examples, how this can be used for KoBoCollect with XLSForm.
For example we managed to use body::jr:noAddRemove as column and set true() for a begin_repeat. But false() didn’t work. Also we could not yet use jr:setvalue.
Or at least a guidance where to find more information for usage would be highly appreciated.
We use XLSForm (Excel) andKoBoCollect with Android phones.
Thanks in advance.
Best regards