use warnings;
use strict;

while (<DATA>){
    my @matches;
	@matches = (/(?<=[%>])%([^%]+)%(?=[%<])/g);
    print join ' ', @matches;
    print "\n";
}

__DATA__
<span color="#231f20" someattr="%do_not_match%" textOverprint="false">%PN1%</span>
<span color="#231f20" someattr="%do_not_match%" textOverprint="false">%DIMMM%%DIMINCH%</span>

__END__
PN1
DIMMM DIMINCH