Whitespace is no longer a valid delimiter (older Perls allowed it), and there are already measures taken to advance past the whitespace. In addition, " " is not a special case character like the brackets are. Therefore, I'll hazard a guess and say they're in there for readability. And because 5 is such a better offset than 4.

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Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;