When it's easier to talk about what you want to keep than what you want to throw away, then it's time to use m//g instead of split. I'd start with something like:

my @pieces = m/\G(<[^>]*>|#[^#]*#|[^#<]+)/g;
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No error checking here. If you wanted error checking, inch along until pos() is at the end of the string, or take the error if it's not and there's no match. Something like:

pos = 0;
while (m/\G(<[^>]*>|#[^#]*#|[^#<]+)/gc) {
  push @pieces, $1;
}
die unless pos >= length;
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It would be nice if list-context m//gc left pos at the last match, but last I checked it was still broken.

-- Randal L. Schwartz, Perl hacker