After discussion, LGPL seems to be the correct license

LICENSE

@@ -1,21 +1,16 @@
-MIT License
+CLI11: A command line parser for C++11
+Copyright (C) 2017 Henry Schreiner
 
-Copyright (c) 2017 Henry Schreiner
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License as published by the Free Software Foundation; either
+version 2.1 of the License, or (at your option) any later version.
 
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Lesser General Public License for more details.
 
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+You should have received a copy of the GNU Lesser General Public
+License along with this library; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

README.md

@@ -1,6 +1,6 @@
 [![Build Status](https://travis-ci.org/henryiii/CLI11.svg?branch=master)](https://travis-ci.org/henryiii/CLI11)
 [![Join the chat at https://gitter.im/CLI11gitter/Lobby](https://badges.gitter.im/CLI11gitter/Lobby.svg)](https://gitter.im/CLI11gitter/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](./LICENSE)
+[![License: LGPL v2.1](https://img.shields.io/badge/License-LGPL%20v2.1-blue.svg)](./LICENSE)
 
 # CLI11: Command line parser for C++11
 

include/CLI/App.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <string>

include/CLI/CLI.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 // CLI Library includes

include/CLI/Error.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <string>

include/CLI/Ini.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <fstream>

include/CLI/Option.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <string>

include/CLI/Split.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <string>

include/CLI/StringTools.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <string>

include/CLI/TypeTools.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <vector>

include/CLI/Validators.hpp

@@ -1,6 +1,6 @@
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 #include <string>

scripts/MakeSingleHeader.py

@@ -38,7 +38,7 @@ def MakeHeader(out):
     output = '''\
 #pragma once
 
-// Distributed under the MIT license.  See accompanying
+// Distributed under the LGPL v2.1 license.  See accompanying
 // file LICENSE or https://github.com/henryiii/CLI11 for details.
 
 // This file was generated using MakeSingleHeader.py in CLI11/scripts