That's not really a good argument because in any programming language with quoted string, the \ is usually a meta character interpreted to escape a quote: "stri\"ng".
The & usage is actually shown in the help file with the example for creating menu, but it's not described at all.
Wikichip didn't have anything about it, I added mIRC's example here:
https://en.wikichip.org/wiki/mirc/dialogs#Mnemonic
