user_func => sub {
        # worker chunk routine
        my ($mce, $chunk_ref, $chunk_id) = @_;

        $$chunk_ref =~ tr/-!"#%&'()*,.\/:;?@\[\\\]_{}0123456789//d;
        $$chunk_ref =~ s/w(as|ere)/be/gi;
        $$chunk_ref =~ s/$RE1/ $W1{lc $1} /g;
        $$chunk_ref =~ s/$RE2/ $W2{lc $1} /g;
        $$chunk_ref =~ s/$RE3/ $W3{lc $1} /g;

        # Output orderly and serially.
        MCE->relay_lock;
        print $OUT_FH $$chunk_ref; $OUT_FH->flush;
        MCE->relay_unlock;
    }