A proof of execution by subscribing witness is an indirect act: the principal never appears, and the notary certifies the execution on the strength of what a witness swears to. Because the principal is absent, the oath must establish the whole chain. The subscribing witness swears that the person named in the document is the one who executed it, that the witness saw the execution or the acknowledgment of it, that the witness signed as a witness at the principal's request, and that the principal requested them to do so. That last element is what distinguishes a subscribing witness from a bystander who happened to observe: it establishes that the principal knowingly invoked the witness's participation, which is part of what makes the indirect certification safe. The act carries a further safeguard — the subscribing witness must be identified by a credible witness personally known to the notary, not by identification documents — and California limits the documents on which a proof may be used.