Manipulate the Chat

[stAjora]

I'm looking at the chat functions and I was wondering what the extra chat channels are for and how do you access/use them? http://wiki.esoui.com/Globals#MsgChannelType
CHAT_CHANNEL_USER_CHANNEL_1
CHAT_CHANNEL_USER_CHANNEL_2
CHAT_CHANNEL_USER_CHANNEL_3
etc

Is there a way for an add on to BLOCK a message from appearing? (I know there is probably a in game IGNORE) but for design purposes, what would blocking a message from a particular player look like in an add on?