If he does,if he is tried by a competent court,if he is told and clearly understands the nature of the offence for which he is being tried,if the case against him is fully and fairly explained to him and he is afforded a full and fair opportunity of defending himself,then,provided there is 'substantial' compliance with the outward forms of the law,mere mistakes in procedure,mere inconsequential errors and omissions in the trial are regarded as venal by the Code and the trial is not vitiated unless the accused can show substantial prejudice