I'd go with 

(?<!\S)

[download]

so 

s/[^\S \n]//g;
s/(?<!\S) +| +(?!\S)//g;
s/\n\n\K\n+//g;

[download]

In reply to Re^6: regexp: removing extra whitespace by ikegami
in thread regexp: removing extra whitespace by perlmax

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