$text =~ s/\s+|(STARTPRESERVE.*?STOPPRESERVE)/${[$1,' ']}[!$1]/gs

UPDATE: jeffa, If you think that's twisted, you should see the version for nested START STOP markers:-)

to remove the markers:
s/\s+|STARTPRESERVE(.*?)STOPPRESERVE/${[' ',$1]}[defined $1]/gs

In reply to Re: RegEx to filter \s not between labels by I0
in thread RegEx to filter \s not between labels by gryphon

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