What is a defendant's duty of counsel in a criminal case to instruct a jury on the principles of law relevant to their understanding of the case?

given . . . even though no objection was made thereto in the lower court, if the substantial rights of the defendant were affected thereby." (Pen. Code, 1259.) "'In criminal cases, even in the absence of a request, a trial court must instruct on general principles of law relevant to the issues raised by the evidence and necessary for the jury's understanding of the case.'" (People v. Anderson (2011) 51 Cal.4th 989, 996.) The court's duty extends to defenses supported by substantial evidence (id. at p. 996), a principle which is pertinent here because the Attorney General contends defendant's alleged lack of knowledge that the notes were securities is at most an affirmative defense, not an element of the crime.