However, legally it's not that simple.This file is hereby placed into public domain,
no copyright is claimed.
https://creativecommons.org/public-domain/cc0/Dedicating works to the public domain is difficult if not impossible for those wanting to contribute their works for public use before applicable copyright or database protection terms expire. Few if any jurisdictions have a process for doing so easily and reliably. Laws vary from jurisdiction to jurisdiction as to what rights are automatically granted and how and when they expire or may be voluntarily relinquished. More challenging yet, many legal systems effectively prohibit any attempt by these owners to surrender rights automatically conferred by law, particularly moral rights, even when the author wishing to do so is well informed and resolute about doing so and contributing their work to the public domain.
Creative Commons has created a license that attempts to solve this legally by, as much as possible, legally codifying the intent of a public domain grant. They call the license CC0.
My request is to officially relicense the file as CC0. Bonus points for adding a SPDX-License-Identifier: CC0-1.0 line in the header for SPDX license conformance, though that's a wishlist item I can work around.
Why does this matter? I am writing my own wrapper for makemkvcon and in the reference docs I want to include apdefs.h because of how useful it is. It is my understanding that aligns with the author's intent for the file. I am adding file SPDX copyright attribution for GuinpinSoft inc, however "public domain" does not map to any SPDX license. CC0 is a supported SPDX license.