There seem to be few examples for how to use xmodmap to bind a modifier + some key, to a new key.

E.g. I want to bind left Shift (keycode 50) + ` (keycode 21) to emit a grave accent character:

`

This is the normal behavior for a Norwegian keyboard, but not on a Macbook Pro (running Linux).

I'm using xev to get the keycodes, I can successfully map single key presses (with the help from another post which I cannot find) to get essential other keys, e.g. backspace and dollar sign in this manner:

keycode 134 = ISO_Level3_Shift Multi_key ISO_Level3_Shift Multi_key
keycode 21 = backslash bar

However how do I do:

keycode 50 + keycode 21 = Grave character

This is not the correct syntax but it should make what I want clear.

In general how is a modifier key like shift used correctly in the syntax? Can only modifier keys be used in combinations?

I've tried simple things such as "keycode 50 keycode 21 = A" and "keycode 50 + keycode 21 = A". ("A" is not the character I want, I'm just using it for test purposes).