What is the law of onus?

Could you please clarify what you mean by "the law of onus"? In legal terminology, "onus" often refers to the burden of proof, which is the responsibility of a party in a legal proceeding to present evidence to support their claim or position. However, the phrase "the law of onus" is not a commonly recognized legal term. Are you perhaps referring to a specific legal principle or doctrine related to the burden of proof? If so, could you provide more context or detail about the context in which you encountered this phrase? Alternatively, are you asking about the broader concept of the burden of proof and how it applies in various legal contexts?