Change most public domain parts to 0BSD.

Translations and doc/xz-file-format.txt and doc/lzma-file-format.txt
were not touched.

COPYING.0BSD was added.

1 files changed, 65 insertions, 47 deletions

diff --git a/COPYING b/COPYING
index 7e393aae..4066c93e 100644
--- a/COPYING
+++ b/COPYING
@@ -6,77 +6,95 @@ XZ Utils Licensing
     is a rough summary of which licenses apply to which parts of this
     package (but check the individual files to be sure!):
 
-      - liblzma is in the public domain.
+      - liblzma is under the BSD Zero Clause License (0BSD).
 
-      - xz, xzdec, and lzmadec command line tools are in the public
-        domain unless GNU getopt_long had to be compiled and linked
-        in from the lib directory. The getopt_long code is under
-        GNU LGPLv2.1+.
+      - The command line tools xz, xzdec, lzmadec, and lzmainfo are
+        under 0BSD except that, on systems that don't have a usable
+        getopt_long, GNU getopt_long is compiled and linked in from the
+        'lib' directory. The getopt_long code is under GNU LGPLv2.1+.
 
       - The scripts to grep, diff, and view compressed files have been
-        adapted from gzip. These scripts and their documentation are
-        under GNU GPLv2+.
-
-      - All the documentation in the doc directory and most of the
-        XZ Utils specific documentation files in other directories
-        are in the public domain.
+        adapted from gzip. These scripts (xzgrep, xzdiff, xzless, and
+        xzmore) and their documentation are under GNU GPLv2+. The man
+        page of xzless ('xzless.1') is an exception: it's under 0BSD.
+
+      - Most of the XZ Utils specific documentation that is in
+        plain text files (like README, INSTALL, PACKAGERS, NEWS,
+        and ChangeLog) are under 0BSD unless stated otherwise in
+        the file itself. The files xz-file-format.txt and
+        lzma-file-format.xt are in the public domain but may
+        be distributed under the terms of 0BSD too.
+
+      - Doxygen-generated HTML version of the liblzma API documentation:
+        While Doxygen is under the GNU GPLv2, the license information
+        in Doxygen includes the following exception:
+
+            Documents produced by doxygen are derivative works
+            derived from the input used in their production;
+            they are not affected by this license.
 
         Note: The JavaScript files (under the MIT license) have
-        been removed from the Doxygen-generated HTML version of the
-        liblzma API documentation. Doxygen itself is under the GNU GPL
-        but the remaining files generated by Doxygen are not affected
-        by the licenses used in Doxygen because Doxygen licensing has
-        the following exception:
+        been removed from the Doxygen output.
 
-            "Documents produced by doxygen are derivative works
-            derived from the input used in their production;
-            they are not affected by this license."
+      - The XZ logo (xz-logo.png) included in the Doxygen-generated
+        documentation is under the Creative Commons BY-SA 4.0 license.
 
-      - The XZ logo included in the Doxygen documentation is under
-        the Creative Commons BY-SA 4.0 license.
+      - Translated messages and man pages are under 0BSD except that
+        some old translations are in the public domain.
 
-      - Translated messages are in the public domain.
+      - Test files and test code in the 'tests' directory, and
+        debugging utilities in the 'debug' directory are under
+        the BSD Zero Clause License (0BSD).
 
-      - The build system contains public domain files, and files that
-        are under GNU GPLv2+ or GNU GPLv3+. None of these files end up
-        in the binaries being built.
+      - The GNU Autotools based build system contains files that are
+        under GNU GPLv2+, GNU GPLv3+, and a few permissive licenses.
+        These files don't affect the licensing of the binaries being
+        built.
 
-      - Test files and test code in the tests directory, and debugging
-        utilities in the debug directory are in the public domain.
+      - The extra directory contain files that are under various
+        free software licenses.
 
-      - The extra directory may contain public domain files, and files
-        that are under various free software licenses.
+    For the files under the BSD Zero Clause License (0BSD), if
+    a copyright notice is needed, the following is sufficient:
 
-    You can do whatever you want with the files that have been put into
-    the public domain. If you find public domain legally problematic,
-    take the previous sentence as a license grant. If you still find
-    the lack of copyright legally problematic, you have too many
-    lawyers.
+        Copyright (C) The XZ Utils authors and contributors
 
-    As usual, this software is provided "as is", without any warranty.
-
-    If you copy significant amounts of public domain code from XZ Utils
+    If you copy significant amounts of 0BSD-licensed code from XZ Utils
     into your project, acknowledging this somewhere in your software is
     polite (especially if it is proprietary, non-free software), but
-    naturally it is not legally required. Here is an example of a good
-    notice to put into "about box" or into documentation:
+    it is not legally required by the license terms. Here is an example
+    of a good notice to put into "about box" or into documentation:
 
         This software includes code from XZ Utils
         <https://xz.tukaani.org/xz-utils/>.
 
     The following license texts are included in the following files:
+      - COPYING.0BSD: BSD Zero Clause License
       - COPYING.LGPLv2.1: GNU Lesser General Public License version 2.1
       - COPYING.GPLv2: GNU General Public License version 2
       - COPYING.GPLv3: GNU General Public License version 3
       - COPYING.CC-BY-SA-4.0: Creative Commons Attribution-ShareAlike 4.0
                               International Public License
 
-    Note that the toolchain (compiler, linker etc.) may add some code
-    pieces that are copyrighted. Thus, it is possible that e.g. liblzma
-    binary wouldn't actually be in the public domain in its entirety
-    even though it contains no copyrighted code from the XZ Utils source
-    package.
-
-    If you have questions, don't hesitate to ask the author(s) for more
-    information.
+    A note about old XZ Utils releases:
+
+        XZ Utils releases 5.4.6 and older and 5.5.1alpha have a
+        significant amount of code put into the public domain and
+        that obviously remains so. The switch from public domain to
+        0BSD for newer releases was made in Febrary 2024 because
+        public domain has (real or perceived) legal ambiguities in
+        some jurisdictions.
+
+        There is very little *practical* difference between public
+        domain and 0BSD. The main difference likely is that one
+        shouldn't claim that 0BSD-licensed code is in the public
+        domain; 0BSD-licensed code is copyrighted but available under
+        an extremely permissive license. Neither 0BSD nor public domain
+        require retaining or reproducing author, copyright holder, or
+        license notices when distributing the software. (Compare to,
+        for example, BSD 2-Clause "Simplified" License which does have
+        such requirements.)
+
+    If you have questions, don't hesitate to ask for more information.
+    The contact information is in the README file.