[VIM] Replacing text with the return value of a function

In VIM, when using the substitute command (:s), it is possible to call a function in the replace part of the :s command. This is the case when the replace part starts with a \=, like shown here

:s/REGEXP/\=SomeFunc()/

The following substitute replaces each character with the second next character in the alphabeth...

:%s/\(\w\)/\=nr2char(char2nr(submatch(1))+2)/g

... so, a

abcdef

... is turned into a

cdefgh