In the channel menu is /addban <parameters> but as far as I can see there is no help for the needed syntax.

If one wants to set an IP or a range of IPs to "silent", how is that done?

/addban 1.2.3.4/32 silent
6:05:40 PM Invalid ban string.  Press F1 for help.

F1 doesn't help at all as most channel level promotion/restrictions are undocumented and there is no command-line syntax that I could find.

have you tried not putting silent at the end?

yes... and it resulted in the same error
another pesky undocumented feature.. just need to know the expected syntax