# Token is sent with form.
my $token = md5_hex(join("",sort $row->get_columns));

if ( $token eq $c->request->body_params->{token} )
{
    # Record hasn't been updated by anyone since the form was loaded.
    # Continue with edit/update...
}
else
{
    # Warn about edit collision, pretty format diffs/choices
    # with Algorithm::Diff/Algorithm::Diff::Apply.
}