In common law systems, one feature that distinguishes a trial "de novo" from an appellate proceeding is that new evidence may not ordinarily be presented in an appeal (though there are rare instances when it may be allowed—usually evidence that came to light only after the trial and could not, in all diligence, have been presented in the lower court). The general rule, is that an appeal must be based solely on "points of law", and not on "points of fact". Appeals are frequently based on a claim that the trial judge or jury did not allow or appreciate all the facts; if that claim is successful the appeal judges will often order a trial "de novo". In order to protect the individual's rights against double jeopardy, ordering a trial "de novo" is often the exclusive right of an appeal judge.