xkb swap backslash and return: how to deal with shift?

I'm trying to swap Enter and Backslash key. I figured out how to swap them when Shift is not involved: key {[ backslash ]}; key {[ Return ]}; However, when shift is down, by pressing Enter I got "\", whereas I would like to have "|" there. And vice versa, by pressing Backslash I got "|", whereas I would like to have Enter (just as without shift). How to define keys for Shift? Any help would be greatly appreciated!