Standardize project licensing on BSD-3-Clause

Align LICENSE, gemspec, and README to BSD-3-Clause and add the
non-endorsement clause to the project license text.

Normalize missing spec file headers to the standard BSD-3 license
block for repository-wide consistency.

Document the motivation in CHANGELOG and README (License Change FAQ)
to prevent endorsement misrepresentation; no API/runtime behavior
changes.

Author: evolve75

CHANGELOG.md

@@ -8,6 +8,9 @@ Changes section to scan for breaking or behavioral changes.
 
 ### 3.0.0pre / 2026-02-10
 
+* Standardize project licensing text on BSD-3-Clause and add an explicit
+  non-endorsement clause to prevent misrepresentation of maintainer/project
+  endorsement in derived products.
 * Rationalize RSpec coverage for core tree families so specs emphasize common
   API usage readability, while exhaustive edge-case and regression coverage
   remains in the Test::Unit suite.

LICENSE.md

@@ -1,4 +1,4 @@
-[RubyTree][]  is licensed under the [BSD-2-clause][] license.
+[RubyTree][]  is licensed under the [BSD-3-clause][] license.
 
 Copyright (c) 2006-2026 Anupam Sengupta (<https://github.com/evolve75>).
 
@@ -12,6 +12,10 @@ are permitted provided that the following conditions are met:
     this list of conditions and the following disclaimer in the documentation
     and/or other materials provided with the distribution.
 
+3. Neither the name of the organization nor the names of its contributors may
+    be used to endorse or promote products derived from this software without
+    specific prior written permission.
+
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
@@ -23,5 +27,5 @@ ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-[BSD-2-clause]: https://opensource.org/license/bsd-2-clause/ "BSD License"
+[BSD-3-clause]: https://opensource.org/license/bsd-3-clause/ "BSD License"
 [RubyTree]:     http://rubytree.anupamsg.me/ "RubyTree Home Page"

README.md

@@ -71,7 +71,7 @@ supports the Ruby's standard object [marshaling][].
 Note: `Marshal.load` and `JSON.parse(..., create_additions: true)` can execute
 code or instantiate objects; do not use them with untrusted input.
 
-This is a [BSD licensed][BSD] open source project, and is hosted at
+This is a [BSD-3 licensed][BSD] open source project, and is hosted at
 [github.com/evolve75/RubyTree][rt@github], and is available as a standard gem
 from [rubygems.org/gems/rubytree][rt_gem].
 
@@ -253,7 +253,25 @@ A big thanks to the following contributors for helping improve **RubyTree**:
 **RubyTree** is licensed under the terms of the [BSD][] license. See
 [LICENSE.md](./LICENSE.md) for details.
 
-[BSD]:https://opensource.org/licenses/bsd-license.php
+### License Change FAQ
+
+1. What changed?
+   RubyTree now standardizes on BSD-3-Clause.
+
+2. Why was this changed?
+   BSD-3-Clause adds an explicit non-endorsement clause to prevent
+   misrepresentation, so third parties cannot imply maintainer or project
+   endorsement of derived products without prior written permission.
+
+3. Does this impact end users of the gem?
+   There is no runtime or API impact for gem users. This is a legal/compliance
+   clarification only.
+
+4. Does this impact redistributors or downstream packages?
+   Redistributors should continue to retain copyright and disclaimer text and
+   must not imply endorsement by RubyTree maintainers/contributors.
+
+[BSD]:https://opensource.org/license/bsd-3-clause/
 [Binary tree]:https://en.wikipedia.org/wiki/Binary_tree
 [Binary Heap]:https://en.wikipedia.org/wiki/Binary_heap
 [Binary Max Heap]:https://en.wikipedia.org/wiki/Binary_heap

rubytree.gemspec

@@ -12,7 +12,7 @@ require File.join(__dir__, '/lib/tree/version')
 Gem::Specification.new do |s|
   s.name                  = 'rubytree'
   s.version               = Tree::VERSION
-  s.license               = 'BSD-2-Clause'
+  s.license               = 'BSD-3-Clause'
   # NOTE: s.date should NOT be assigned. It is automatically set to pkg date.
   s.platform              = Gem::Platform::RUBY
   s.author                = 'Anupam Sengupta'

spec/spec_helper.rb

@@ -1,3 +1,32 @@
+# spec_helper.rb - This file is part of the RubyTree package.
+#
+# Copyright (c) 2026 Anupam Sengupta. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# - Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# - Neither the name of the organization nor the names of its contributors may
+#   be used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 # spec_helper.rb
 #
 # Author:  Anupam Sengupta

spec/tree/aa_tree_spec.rb

@@ -1,3 +1,32 @@
+# aa_tree_spec.rb - This file is part of the RubyTree package.
+#
+# Copyright (c) 2026 Anupam Sengupta. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# - Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# - Neither the name of the organization nor the names of its contributors may
+#   be used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 # frozen_string_literal: true
 
 require 'rspec'

spec/tree/avl_tree_node_spec.rb

@@ -1,3 +1,32 @@
+# avl_tree_node_spec.rb - This file is part of the RubyTree package.
+#
+# Copyright (c) 2026 Anupam Sengupta. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# - Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# - Neither the name of the organization nor the names of its contributors may
+#   be used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 # frozen_string_literal: true
 
 require 'rspec'

spec/tree/b_tree_spec.rb

@@ -1,3 +1,32 @@
+# b_tree_spec.rb - This file is part of the RubyTree package.
+#
+# Copyright (c) 2026 Anupam Sengupta. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# - Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# - Neither the name of the organization nor the names of its contributors may
+#   be used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 # frozen_string_literal: true
 
 require 'rspec'

spec/tree/binary_heap_node_spec.rb

@@ -1,3 +1,32 @@
+# binary_heap_node_spec.rb - This file is part of the RubyTree package.
+#
+# Copyright (c) 2026 Anupam Sengupta. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# - Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# - Neither the name of the organization nor the names of its contributors may
+#   be used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 # frozen_string_literal: true
 
 require 'rspec'

spec/tree/binary_max_heap_node_spec.rb

@@ -1,3 +1,32 @@
+# binary_max_heap_node_spec.rb - This file is part of the RubyTree package.
+#
+# Copyright (c) 2026 Anupam Sengupta. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# - Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# - Redistributions in binary form must reproduce the above copyright notice, this
+#   list of conditions and the following disclaimer in the documentation and/or
+#   other materials provided with the distribution.
+#
+# - Neither the name of the organization nor the names of its contributors may
+#   be used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+#   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
 # frozen_string_literal: true
 
 require 'rspec'