If you want to put the x inside the regex you can do it like this (ripping off Utilitarian's code):

my $regex =qr{(?x)
    ^(\w*)?\s         #A comment
    (\w*)?\s          # an other 
    (\w*)?\s          # and again
    (?:([A-Z]*)\s)?   # all the way through
    (\d+)\*           # so that the homicidal psychopath
    (?:([0-9+]+)[>])? # who knows where you live
    ([0-9+]+)\s.      # and will have to maintain this code
    (\d*)             # will think well of you
    };
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Note that the (?x) must immediately follow the first regex delimiter otherwise the whitespace before will be a literal part of the pattern (this was not the case with earlier Perl versions, 5.6 IIRC) and note also that using qr{...} creates a compiled regex which you assign to a scalar for later use. The nice thing about the (?x) syntax is the ability to switch behaviours on and off for different regions in your pattern whereas the /.../x modifier applies to the whole pattern. This is probably more useful with something like case insensitivity and such use is illustrated in this reply in a thread started by Win.

I hope this is helpful.