Except as provided in Rule 269 the plaintiff shall have the right to open and conclude both in adducing his evidence and in the argument, unless the burden of proof on the whole case under the pleadings rests upon the defendant, or unless the defendant or all of the defendants, if there should be more than one, shall, after the issues of fact are settled and before the trial commences, admit that the plaintiff is entitled to recover as set forth in the petition, except so far as he may be defeated, in whole or in part, by the allegations of the answer constituting a good defense, which may be established on the trial; which admission shall be entered of record, whereupon the defendant, or the defendants, if more than one, shall have the right to open and conclude in adducing the evidence and in the argument of the cause. The admission shall not serve to admit any allegation which is inconsistent with such defense, which defense shall be one that defendant has the burden of establishing, as for example, and without excluding other defenses: accord and satisfaction, adverse possession, arbitration and award, contributory negligence, discharge in bankruptcy, duress, estoppel, failure of consideration, fraud, release, res judicata, statute of frauds, statute of limitations, waiver, and the like.