Some events, like ON TEXT do allow the usage of #,?
If you look in the help file under /help ON TEXT you'll see that it shows
Format: on <level>:TEXT:<matchtext>:<*><?><#[,#]>:<commands>
The fact that the <#,[#]> indicates that more than one channel can be specified, and the fact that the ? is listed as a separate option, means that the two can be combined, as opposed to the format for ON INPUT which shows as
which indicates that only one of those options can be used at a time.