bip3: Switch to SPDX identifiers

bip-0003.md

@@ -120,8 +120,8 @@ appear in the following order. Headers marked with "\*" are optional. All other
   Status: <Draft | Complete | Deployed | Closed>
   Type: <Specification | Informational | Process>
   Created: <Date of number assignment (yyyy-mm-dd), or "?">
-  License: <Identifier(s) of acceptable license(s)>
-* License-Code: <Identifier(s) for Code under different acceptable license(s)>
+  License: <SPDX License Expression>
+* License-Code: <SPDX License Expression for Code (if different)>
 * Discussion: <Noteworthy discussion threads in "yyyy-mm-dd: URL" format>
 * Version: <MAJOR.MINOR.PATCH>
 * Requires: <BIP number(s)>
@@ -147,10 +147,8 @@ appear in the following order. Headers marked with "\*" are optional. All other
   Authors header. See the [BIP Ownership](#bip-ownership) section above.
 * Status — The stage of the workflow of the proposal. See the [Workflow](#workflow) section below.
 * Type — See the [BIP Types](#bip-types) section below for a description of the three BIP types.
-* License and License-Code — These headers list SPDX License Identifier(s) of the acceptable licenses under which the
-  BIP and corresponding code are available. See the [BIP Licensing](#bip-licensing) section below for a description of
-  the Licenses and their SPDX License Identifiers. If there are multiple acceptable licenses, each should be on a
-  separate line.
+* License and License-Code — These headers specify SPDX License Expressions describing the licenses under which the
+  BIP and corresponding code are available. See the [BIP Licensing](#bip-licensing) section below.
 * Discussion — The Discussion header points the audience to relevant discussions of the BIP, e.g., the mailing list
   thread in which the idea for the BIP was discussed, a thread where a new version of the BIP was presented, or relevant
   discussion threads on other platforms. Entries take the format "yyyy-mm-dd: URL", e.g., `2009-01-09:
@@ -391,67 +389,69 @@ innovate on a level playing field. Only freely licensed contributions are accept
 
 ### Specification
 
-Each new BIP must identify at least one acceptable license in its preamble. Licenses must be referenced per their
-respective [SPDX License identifier](https://spdx.org/licenses). New BIPs may be accepted with the licenses described
-below.
+Each new BIP must specify in two ways under which license terms it is made available. First, it must specify an [SPDX
+License Expression](https://spdx.dev/ids/) in the License field in the preamble. Second, it must include a matching
+Copyright section, possibly providing further details on licensing.
 
 For example, a preamble might include the following License header:
 
-    License: CC0-1.0
-             GNU-All-Permissive
+    License: CC0-1.0 OR MIT
 
-In this case, the BIP text is fully licensed under both the Creative Commons CC0 1.0 Universal license as well as the
-GNU All-Permissive License, and anyone may modify and redistribute the text provided they comply with the terms of
-*either* license. In other words, the license list is an "OR choice", not an "AND also" requirement.
+In this case, the BIP (including all auxiliary files) is made available under the terms of both Creative Commons CC0 1.0 Universal as well as the
+MIT License, and anyone may modify and redistribute it provided they comply with the terms of
+*either* license, at their option. In other words, the license list is an "OR choice", not an "AND also" requirement. See the [SPDX
+documentation](https://spdx.dev/ids/) and the [SPDX License List](https://spdx.org/licenses/) for further details.
 
-It is also possible to license source code differently from the BIP text by including the optional License-Code header
-after the License header. Again, each license must be referenced by their respective SPDX License identifier shown
-below.
+It is also possible to specify that source code is licensed differently by including the optional License-Code header
+after the License header. Again, the licensing terms must be specified using an SPDX License Expression.
 
-Each source code file or source directory should specify the license under which it is made available as is common in
-software (e.g., with a license header or a LICENSE/COPYING file). It is recommended to make any test vectors available
-under CC0-1.0 or GNU-All-Permissive in addition to any other licenses to allow anyone to copy test vectors into their
-implementations without introducing license hindrances. Licenses listed in the License-Code header apply to all source
-directories, source code files, and test vectors provided with the BIP except those where a LICENSE file in a directory
+Each auxiliary source code file or source directory should specify the license under which it is made available as is common in
+software (e.g., with a [`SPDX-License-Identifier: <SPDX License Expression>` comment](https://spdx.dev/ids/),
+a license header, or a LICENSE/COPYING file). It is recommended to make any test vectors available
+under CC0-1.0 or FSFAP in addition to any other licenses to allow anyone to copy test vectors into their
+implementations without introducing license hindrances. Licenses listed in the License-Code header apply to all source directories,
+source code files, and test vectors provided with the BIP except those where a LICENSE file in a directory
 or the file header states otherwise.
 
 For example, a preamble specifying the optional License-Code header might look like:
 
     License:         CC0-1.0
     License-Code:    MIT
 
-In this case, the code in the BIP is not available under CC0-1.0, but is only available under the terms of the MIT
+In this case, the source code in the BIP is not available under Creative Commons CC0 1.0 Universal, but is only available under the MIT
 License.
 
-BIPs are not required to be *exclusively* licensed under approved terms, and may also be licensed under unacceptable
-licenses *in addition to* at least one acceptable license. In this case, only the acceptable license(s) should be listed
-in the License and License-Code headers.
-
-It is recommended that BIPs that include literal code be licensed under the same license terms as the project it
-modifies. For example, literal code intended for Bitcoin Core would ideally be licensed (or dual-licensed) under the MIT
-license terms.
+It is recommended that source code included in a BIP (whether within the text or in auxiliary files) be licensed under the same license terms as the project it
+is proposed to modify, if any. For example, changes intended for Bitcoin Core would ideally be licensed (also) under the MIT
+License.
 
 In all cases, details of the licensing terms must be provided in the Copyright section of the BIP.
 
 #### Acceptable Licenses[^licenses]
 
-* BSD-2-Clause: [OSI-approved BSD 2-clause license](https://opensource.org/licenses/BSD-2-Clause)
-* BSD-3-Clause: [OSI-approved BSD 3-clause license](https://opensource.org/licenses/BSD-3-Clause)
+Each new BIP must be made available under at least one acceptable license as listed below. BIPs are not required to be
+*exclusively* licensed under approved terms, and may also be licensed under other licenses *in addition to* at least one
+acceptable license.
+
+In other words, a new BIP must specify an SPDX License Expression that is either "L" or equivalent to "L OR E" for some
+acceptable license L from the following list and another SPDX License Expression E.
+
+* BSD-2-Clause: [BSD 2-Clause License](https://opensource.org/licenses/BSD-2-Clause)
+* BSD-3-Clause: [BSD 3-Clause License](https://opensource.org/licenses/BSD-3-Clause)
 * CC0-1.0: [Creative Commons CC0 1.0 Universal](https://creativecommons.org/publicdomain/zero/1.0/)
-* GNU-All-Permissive: [GNU All-Permissive License](http://www.gnu.org/prep/maintain/html_node/License-Notices-for-Other-Files.html)
+* FSFAP: [FSF All Permissive License](https://www.gnu.org/prep/maintain/html_node/License-Notices-for-Other-Files.html)
 * CC-BY-4.0: [Creative Commons Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)
-* MIT: [Expat/MIT/X11 license](https://opensource.org/licenses/MIT)
-* Apache-2.0: [Apache License, version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
-* BSL-1.0: [Boost Software License, version 1.0](http://www.boost.org/LICENSE_1_0.txt)
+* MIT: [Expat/MIT/X11 License](https://opensource.org/licenses/MIT)
+* Apache-2.0: [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0)
+* BSL-1.0: [Boost Software License 1.0](https://www.boost.org/LICENSE_1_0.txt)
 
 #### Not Acceptable Licenses
 
 All licenses not explicitly included in the above lists are not acceptable terms for a Bitcoin Improvement Proposal.
-However, BIPs predating this proposal were allowed under other terms, and should use these abbreviations
-when no other license is granted:
+However, BIPs predating this proposal were accepted under other terms, and should use one the following identifiers.
 
-* PD: Released into the public domain
-* OPL: [Open Publication License, version 1.0](http://opencontent.org/openpub/)
+* LicenseRef-PD: Placed into the public domain
+* OPUBL-1.0: [Open Publication License 1.0](https://opencontent.org/openpub/)
 
 ## BIP Editors
 
@@ -734,9 +734,9 @@ feedback, and helpful comments.
     * PD: 42
     * CC0-1.0: 23
     * BSD-3-Clause: 19
-    * OPL: 5
+    * OPUBL-1.0: 5
     * CC-BY-SA-4.0: 4
-    * GNU-All-Permissive: 3
+    * FSFAP: 3
     * MIT: 2
     * CC-BY-4.0: 1
 
@@ -747,15 +747,15 @@ feedback, and helpful comments.
     The following previously acceptable licenses were retained per request of reviewers, even though they have so far
     never been used in the BIPs process:
 
-    * Apache-2.0: [Apache License, version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
-    * BSL-1.0: [Boost Software License, version 1.0](http://www.boost.org/LICENSE_1_0.txt)
+    * Apache-2.0: [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0)
+    * BSL-1.0: [Boost Software License 1.0](https://www.boost.org/LICENSE_1_0.txt)
 
     The following previously acceptable licenses have never been used in the BIPs Process and have been dropped:
 
-    * AGPL-3.0+: [GNU Affero General Public License (AGPL), version 3 or newer](http://www.gnu.org/licenses/agpl-3.0.en.html)
-    * FDL-1.3: [GNU Free Documentation License, version 1.3](http://www.gnu.org/licenses/fdl-1.3.en.html)
-    * GPL-2.0+: [GNU General Public License (GPL), version 2 or newer](http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html)
-    * LGPL-2.1+: [GNU Lesser General Public License (LGPL), version 2.1 or newer](http://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html)
+    * AGPL-3.0+: [GNU Affero General Public License (AGPL) 3](https://www.gnu.org/licenses/agpl-3.0.en.html)
+    * FDL-1.3: [GNU Free Documentation License 1.3](https://www.gnu.org/licenses/fdl-1.3.en.html)
+    * GPL-2.0+: [GNU General Public License (GPL) 2 or newer](https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html)
+    * LGPL-2.1+: [GNU Lesser General Public License (LGPL) 2.1 or newer](https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html)
 
     Why are software licenses included?
 
@@ -772,7 +772,7 @@ feedback, and helpful comments.
       and therefore CC-BY-SA-4.0 (and the GPL-flavors) is no longer considered acceptable for new BIPs. As mentioned
       above, existing BIPs will retain their original licensing.
 
-    Why are OPL and Public Domain no longer acceptable for new BIPs?
+    Why are Open Publication License and Public Domain no longer acceptable for new BIPs?
 
     * Public domain is not universally recognised as a legitimate action, thus it is inadvisable.
-    * The OPL is generally regarded as obsolete, and not a license suitable for new publications.
+    * The Open Publication License is generally regarded as obsolete, and not a license suitable for new publications.