How about a oneliner and no regexes :-) 
perl -lne "print $first++? q{</div><div>}:q{<div>} and next if 0==inde
+x $_, "[Sidenote"; print; print q{</div>} if eof" letters.txt

[download]
print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});

In reply to Re: Regexing a block of text in between patterns by codeacrobat
in thread Regexing a block of text in between patterns by Anonymous Monk

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