Nevertheless, Rule 2 applies here: several months ago we decided it was okay for Perl 6 to allow a conditional modifier inside a loop modifier because it makes it easier to write list comprehensions close to the way mathematicians like to write them:
%desc{$_} if .path for <n ne e se s sw w nw up down>
Also, any parenthesized or bracketed expression is now parsed as a statement, so you can nest modifiers to your heart's content as long as you parenthesize. In particular, this allows you to use a list comprehension for a slice subscript.
Update: changed @desc to %desc as noted by wolverian++
