/usr/include/root/Reflex/ is in libroot-core-dev 5.34.19+dfsg-1.2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/root/Reflex/Any.h
/usr/include/root/Reflex/Base.h
/usr/include/root/Reflex/Builder/
/usr/include/root/Reflex/Builder/ClassBuilder.h
/usr/include/root/Reflex/Builder/CollectionProxy.h
/usr/include/root/Reflex/Builder/DictSelection.h
/usr/include/root/Reflex/Builder/EnumBuilder.h
/usr/include/root/Reflex/Builder/FunctionBuilder.h
/usr/include/root/Reflex/Builder/GenreflexMemberBuilder.h
/usr/include/root/Reflex/Builder/NamespaceBuilder.h
/usr/include/root/Reflex/Builder/NewDelFunctions.h
/usr/include/root/Reflex/Builder/OnDemandBuilder.h
/usr/include/root/Reflex/Builder/OnDemandBuilderForScope.h
/usr/include/root/Reflex/Builder/ReflexBuilder.h
/usr/include/root/Reflex/Builder/TypeBuilder.h
/usr/include/root/Reflex/Builder/TypedefBuilder.h
/usr/include/root/Reflex/Builder/UnionBuilder.h
/usr/include/root/Reflex/Builder/VariableBuilder.h
/usr/include/root/Reflex/Callback.h
/usr/include/root/Reflex/DictionaryGenerator.h
/usr/include/root/Reflex/Kernel.h
/usr/include/root/Reflex/Member.h
/usr/include/root/Reflex/MemberTemplate.h
/usr/include/root/Reflex/Object.h
/usr/include/root/Reflex/PluginService.h
/usr/include/root/Reflex/PropertyList.h
/usr/include/root/Reflex/Reflex.h
/usr/include/root/Reflex/Scope.h
/usr/include/root/Reflex/SharedLibrary.h
/usr/include/root/Reflex/Tools.h
/usr/include/root/Reflex/Type.h
/usr/include/root/Reflex/TypeTemplate.h
/usr/include/root/Reflex/ValueObject.h
/usr/include/root/Reflex/internal/
/usr/include/root/Reflex/internal/BuilderContainer.h
/usr/include/root/Reflex/internal/InternalTools.h
/usr/include/root/Reflex/internal/LiteralString.h
/usr/include/root/Reflex/internal/MemberBase.h
/usr/include/root/Reflex/internal/MemberTemplateImpl.h
/usr/include/root/Reflex/internal/MemberTemplateName.h
/usr/include/root/Reflex/internal/OwnedMember.h
/usr/include/root/Reflex/internal/OwnedMemberTemplate.h
/usr/include/root/Reflex/internal/OwnedPropertyList.h
/usr/include/root/Reflex/internal/PropertyListImpl.h
/usr/include/root/Reflex/internal/ScopeBase.h
/usr/include/root/Reflex/internal/ScopeName.h
/usr/include/root/Reflex/internal/TypeBase.h
/usr/include/root/Reflex/internal/TypeName.h
/usr/include/root/Reflex/internal/TypeTemplateImpl.h
/usr/include/root/Reflex/internal/TypeTemplateName.h