Tried data/defaults.cfg ?

allowspedit means long:allow singleplayer edit, you have to press it together with the E button to edit in Singleplayer.
MOUSE4/5 is the scrollwheel and is used for multiple tasks, for instance if you hold G down while using MOUSE4/5 the gridpower is changed.

I don't know if this is documented somewhere.

OT: Somehow I have to fill in the math question multiple times correctly until it works

Taken from sauerbraten(2008) docs/static_wiki/Scripting Tutorial.html:
modifier-demo
want to handle a script with +X/-X input via mousewheel?
delta_game_42 = [echo we got $arg1 as param "(game)"]
delta_edit_42 = [echo we got $arg1 as param "(edit)"]
bind KP_5 = [domodifier 42]
editbind KP_5 = [domodifier 42]

Do you understand what's going on there? Neither do I!
Maybe this simple example is more helpful:
to bind your own alternative action(s) to the mousewheel, put the following lines in your config:

countup = [ ] // name and content by you
countdown = [ ] // ,,
delta_game_0 = [ if (= $arg1 1) countup countdown ]

// redefines delta_game_0
// to restore see data/defaults.cfg

universaldelta is part of many editing and gaming commands that you're not supposed to play around with until you know you may break something horribly.

delta_edit/game_<num> are special sets of commands executed for certain events, like changing the gridsize or changing weapons. universaldelta merely passes on a value to the corresponding set.