# Restrict row ids to potential or all valid IDs
# -1 1..inf
use constant ROW_ID => { regex => qr/^$RE{num}{int}$/,
                         callbacks => { valid => sub { local $_ = shift;
                                                         $_ == -1
                                                           or $_ >= 1 } } };
# Restrict row ids to things that are actually valid.
# 1 .. inf
use constant VALID_ROW_ID => { regex => qr/^$RE{num}{int}$/,
                               callbacks => { valid => sub { local $_ = shift;
                                                             defined() && $_ >= 1 } } };

sub example_method {
    my $self = shift;
    my %p = validate_pos( @_,
                          { handle => 1,
                            thing  => 1,
                            something_else => VALID_ROW_ID } );
    ...
}