Problems with the MODE command in IRC

As I’ve started to implemented GUI-part of my IRC-client, I’ve started too see some limitations with the handling of the MODE command. One thing that was apparent to me as a user (well, I didn’t think it was anything special) that one can be both voiced and oped at the same time. That is, if you’re initially voiced, then oped and then deoped, you are still voiced. However, if you enter a channel where a user i oped, how do you know if that person is also voiced?