field_filters => { 
     my_filter => sub { my $value = shift; $value =~ s/foo/bar; return $value; },
 },

##</code><code>##

filters => [ sub { my $value = shift; $value =~ s/foo/bar; return $value; } ],

##</code><code>##

sub some_filter_sub {
  my $value = shift;
  $value =~ s/foo/bar;
  return $value;
}
# field_filters => { 
#     my_filter => \&some_filter_sub, 
# },
 filters => [ my_filter => \&some_filter_sub ],