New features in the fish shell

Surprisingly, a condition for if/while consists of a command plus a tail of and/or commands, see https://github.com/fish-shell/fish-shell/blob/master/src/....
This means you can write chained conditions like this:

if cheap-condition; or expensive-condition-part-1; and expensive-condition-part-2
# body goes here
end

Although as a developer I agree that && and || look better.
Using begin/end for grouping allows for more complex conditions.