diff --git a/.xo-callback/.github/workflows/main.yml b/.xo-callback/.github/workflows/main.yml
deleted file mode 100644
index 38eee8cf..00000000
--- a/.xo-callback/.github/workflows/main.yml
+++ /dev/null
@@ -1,98 +0,0 @@
-name: build xo-callback + xo dependencies
-
-on:
-  push:
-    branches: [ "main" ]
-  pull_request:
-    branches: [ "main" ]
-
-env:
-  # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
-  BUILD_TYPE: Release
-
-jobs:
-  build:
-    # The CMake configure and build commands are platform agnostic and should work equally well on Windows or Mac.
-    # You can convert this to a matrix build if you need cross-platform coverage.
-    # See: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
-    runs-on: ubuntu-latest
-
-    steps:
-    - name: checkout source
-      uses: actions/checkout@v3
-
-    - name: Install catch2
-      # install catch2.  see [[https://stackoverflow.com/questions/57982945/how-to-apt-get-install-in-a-github-actions-workflow]]
-      run: sudo apt-get install -y catch2
-
-    # ----------------------------------------------------------------
-
-    - name: Clone xo-cmake
-      uses: actions/checkout@v3
-      with:
-        repository: Rconybea/xo-cmake
-        path: repo/xo-cmake
-
-    - name: Configure xo-cmake
-      run: cmake -B ${{github.workspace}}/build_xo-cmake -DCMAKE_INSTALL_PREFIX=${{github.workspace}}/local repo/xo-cmake
-
-    - name: Build xo-cmake (trivial)
-      run: cmake --build ${{github.workspace}}/build_xo-cmake --config ${{env.BUILD_TYPE}}
-
-    - name: Install xo-cmake
-      run: cmake --install ${{github.workspace}}/build_xo-cmake
-
-    # ----------------------------------------------------------------
-
-    - name: Clone indentlog
-      uses: actions/checkout@v3
-      with:
-        repository: Rconybea/indentlog
-        path: repo/indentlog
-
-    - name: Configure indentlog
-      # configure cmake for indentlog in dedicated build directory.
-      run: cmake -B ${{github.workspace}}/build_indentlog -DCMAKE_MODULE_PATH=${{github.workspace}}/local/share/cmake -DCMAKE_INSTALL_PREFIX=${{github.workspace}}/local repo/indentlog
-
-    - name: Build indentlog
-      run: cmake --build ${{github.workspace}}/build_indentlog --config ${{env.BUILD_TYPE}}
-
-    - name: Install indentlog
-      # install into ${{github.workspace}}/local
-      run: cmake --install ${{github.workspace}}/build_indentlog
-
-    # ----------------------------------------------------------------
-
-    - name: Clone refcnt
-      uses: actions/checkout@v3
-      with:
-        repository: Rconybea/refcnt
-        path: repo/refcnt
-
-    - name: Configure refcnt
-      # configure cmake for refcnt in dedicated build directory.
-      run: cmake -B ${{github.workspace}}/build_refcnt -DCMAKE_MODULE_PATH=${{github.workspace}}/local/share/cmake -DCMAKE_PREFIX_PATH=${{github.workspace}}/local -DCMAKE_INSTALL_PREFIX=${{github.workspace}}/local repo/refcnt
-
-    - name: Build refcnt
-      run: cmake --build ${{github.workspace}}/build_refcnt --config ${{env.BUILD_TYPE}}
-
-    - name: Install refcnt
-      # install into ${{github.workspace}}/local
-      run: cmake --install ${{github.workspace}}/build_refcnt
-
-    # ----------------------------------------------------------------
-
-    - name: Configure self (callback)
-      # Configure CMake in a 'build' subdirectory. `CMAKE_BUILD_TYPE` is only required if you are using a single-configuration generator such as make.
-      # See https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html?highlight=cmake_build_type
-      run: cmake -B ${{github.workspace}}/build_callback -DCMAKE_MODULE_PATH=${{github.workspace}}/local/share/cmake -DCMAKE_PREFIX_PATH=${{github.workspace}}/local -DCMAKE_INSTALL_PREFIX=${{github.workspace}}/local -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}}
-
-    - name: Build self (callback)
-      # Build your program with the given configuration
-      run: cmake --build ${{github.workspace}}/build_callback --config ${{env.BUILD_TYPE}}
-
-    - name: Test self (callback)
-      working-directory: ${{github.workspace}}/build_callback
-      # Execute tests defined by the CMake configuration.
-      # See https://cmake.org/cmake/help/latest/manual/ctest.1.html for more detail
-      run: ctest -C ${{env.BUILD_TYPE}}
diff --git a/.xo-callback/.gitignore b/.xo-callback/.gitignore
deleted file mode 100644
index 132925c0..00000000
--- a/.xo-callback/.gitignore
+++ /dev/null
@@ -1,6 +0,0 @@
-# symlink to path/to/build/compile_commands.json should be manual
-compile_commands.json
-# lsp keeps state here
-.cache
-# typical build directories
-.build*
diff --git a/.xo-callback/CMakeLists.txt b/.xo-callback/CMakeLists.txt
deleted file mode 100644
index 17d73eb3..00000000
--- a/.xo-callback/CMakeLists.txt
+++ /dev/null
@@ -1,31 +0,0 @@
-# callback/CMakeLists.txt
-
-cmake_minimum_required(VERSION 3.10)
-
-project(callback VERSION 0.1)
-
-include(GNUInstallDirs)
-include(cmake/xo-bootstrap-macros.cmake)
-
-xo_cxx_toplevel_options3()
-
-# ----------------------------------------------------------------
-# common c++ settings
-
-# PROJECT_CXX_FLAGS: bespoke for this project - usually empty
-set(PROJECT_CXX_FLAGS "")
-#set(PROJECT_CXX_FLAGS "-fconcepts-diagnostics-depth=2")
-add_definitions(${PROJECT_CXX_FLAGS})
-
-# ----------------------------------------------------------------
-# sources
-
-add_subdirectory(src/callback)
-#add_subdirectory(utest)
-
-# ----------------------------------------------------------------
-# provide find_package() support
-
-xo_export_cmake_config(${PROJECT_NAME} ${PROJECT_VERSION} ${PROJECT_NAME}Targets)
-
-# end CMakeLists.txt
diff --git a/.xo-callback/README.md b/.xo-callback/README.md
deleted file mode 100644
index 53cc5849..00000000
--- a/.xo-callback/README.md
+++ /dev/null
@@ -1,50 +0,0 @@
-# callback-set with reentrant invocation
-
-Reentrant:
-1. A callback can modify parent callback-set (for example to remove itself),
-   even while being invoked.
-2. Any such re-entrant operations are deferred until callback invocation completes.
-
-## Getting Started
-
-### build + install dependencies
-
-- [github/Rconybea/refcnt](https://github.com/Rconybea/refcnt)
-
-### build + install
-
-```
-$ cd xo-callback
-$ mkdir build
-$ cd build
-$ INSTALL_PREFIX=/usr/local  # or wherever you prefer, e.g. ~/local
-$ cmake \
-    -DCMAKE_MODULE_PATH=${INSTALL_PREFIX}/share/cmake \
-    -DCMAKE_PREFIX_PATH=${INSTALL_PREFIX} \
-    -DCMAKE_INSTALL_PREFIX=${INSTALL_PREFIX} ..
-$ make
-$ make install
-```
-(also see .github/workflows/main.yml)
-
-### build for unit test coverage
-
-```
-$ cd xo-callback
-$ mkdir build-ccov
-$ cd build-ccov
-$ cmake \
-    -DCMAKE_MODULE_PATH=${INSTALL_PREFIX}/share/cmake \
-    -DCMAKE_PREFIX_PATH=${INSTALL_PREFIX} \
-    -DCODE_COVERAGE=ON \
-    -DCMAKE_BUILD_TYPE=Debug ..
-```
-
-### LSP (language server) support
-
-LSP looks for compile commands in the root of the source tree;
-cmake creates them in the root of its build directory.
-```
-$ cd xo-callback
-$ ln -s build/compile_commands.json
-```
diff --git a/.xo-callback/cmake/callbackConfig.cmake.in b/.xo-callback/cmake/callbackConfig.cmake.in
deleted file mode 100644
index d6c98d89..00000000
--- a/.xo-callback/cmake/callbackConfig.cmake.in
+++ /dev/null
@@ -1,7 +0,0 @@
-@PACKAGE_INIT@
-
-include(CMakeFindDependencyMacro)
-find_dependency(refcnt)
-include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
-include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Share.cmake")
-check_required_components("@PROJECT_NAME@")
diff --git a/.xo-callback/cmake/xo-bootstrap-macros.cmake b/.xo-callback/cmake/xo-bootstrap-macros.cmake
deleted file mode 100644
index 592272c0..00000000
--- a/.xo-callback/cmake/xo-bootstrap-macros.cmake
+++ /dev/null
@@ -1,41 +0,0 @@
-# ----------------------------------------------------------------
-# for example:
-#   $ PREFIX=/usr/local   # for example
-#   $ cmake -DCMAKE_MODULE_PATH=prefix -DCMAKE_INSTALL_PREFIX=$PREFIX -B .build
-#
-# will get
-#   CMAKE_MODULE_PATH
-# from xo-cmake-config --cmake-module-path
-#
-# and expect .cmake macros in
-#   CMAKE_MODULE_PATH/xo_macros/xo_cxx.cmake
-# ----------------------------------------------------------------
-
-find_program(XO_CMAKE_CONFIG_EXECUTABLE NAMES xo-cmake-config REQUIRED)
-
-if ("${XO_CMAKE_CONFIG_EXECUTABLE}" STREQUAL "XO_CMAKE_CONFIG_EXECUTABLE-NOT_FOUND")
-    message(FATAL "could not find xo-cmake-config executable")
-endif()
-
-message(STATUS "XO_CMAKE_CONFIG_EXECUTABLE=${XO_CMAKE_CONFIG_EXECUTABLE}")
-
-if (XO_SUBMODULE_BUILD)
-    if (("${CMAKE_MODULE_PATH}" STREQUAL "") OR ("${CMAKE_MODULE_PATH}" STREQUAL prefix))
-        # local version of xo-cmake macros
-        set(CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/xo-cmake/cmake")
-        message(STATUS "CMAKE_MODULE_PATH=${CMAKE_MODULE_PATH}")
-    endif()
-else()
-    if (("${CMAKE_MODULE_PATH}" STREQUAL "") OR ("${CMAKE_MODULE_PATH}" STREQUAL prefix))
-        # default to typical install location for xo-project-macros
-        execute_process(COMMAND ${XO_CMAKE_CONFIG_EXECUTABLE} --cmake-module-path OUTPUT_VARIABLE CMAKE_MODULE_PATH)
-        message(STATUS "CMAKE_MODULE_PATH=${CMAKE_MODULE_PATH}")
-    endif()
-endif()
-
-# needs to have been installed somewhere on CMAKE_MODULE_PATH,
-# (e.g. from xo-cmake with the same value for CMAKE_INSTALL_PREFIX)
-#
-include(xo_macros/xo_cxx)
-
-xo_cxx_bootstrap_message()
diff --git a/.xo-callback/include/xo/callback/CallbackSet.hpp b/.xo-callback/include/xo/callback/CallbackSet.hpp
deleted file mode 100644
index 15e938be..00000000
--- a/.xo-callback/include/xo/callback/CallbackSet.hpp
+++ /dev/null
@@ -1,42 +0,0 @@
-// TOOD: rename to RpCallbackSet
-
-/* @file CallbackSet.hpp */
-
-#pragma once
-
-#include "CallbackSetImpl.hpp"
-
-namespace xo {
-    namespace fn {
-        template<typename NativeFn>
-        using RpCallbackSet = CallbackSetImpl<rp<NativeFn>>;
-
-        /* like RpCallbackSet<NativeFn>,
-         * but also provides overload(s) for operator()(..)
-         */
-        template<typename NativeFn, typename MemberFn>
-        class NotifyCallbackSet : public RpCallbackSet<NativeFn> {
-        public:
-            NotifyCallbackSet(MemberFn fn)
-                : privileged_member_fn_{fn} {}
-
-            template<typename ... Tn>
-            void operator()(Tn&&... args) {
-                this->invoke(this->privileged_member_fn_, args...);
-            }
-
-        private:
-            /** implements NotifyCallbackSet's operator()(...) **/
-            MemberFn privileged_member_fn_;
-        };
-
-        template<typename NativeFn, typename Sret, typename ... Sn>
-        inline NotifyCallbackSet<NativeFn, Sret (NativeFn::*)(Sn...)>
-        make_notify_cbset(Sret (NativeFn::* member_fn)(Sn...)) {
-            return NotifyCallbackSet<NativeFn, Sret (NativeFn::*)(Sn...)>(member_fn);
-        } /*make_notify_cbset*/
-
-    } /*namespace fn*/
-} /*namespace xo*/
-
-/* end CallbackSet.hpp */
diff --git a/.xo-callback/src/callback/CMakeLists.txt b/.xo-callback/src/callback/CMakeLists.txt
deleted file mode 100644
index cfeaf08c..00000000
--- a/.xo-callback/src/callback/CMakeLists.txt
+++ /dev/null
@@ -1,14 +0,0 @@
-# callback/CMakeLists.txt
-
-set(SELF_LIB callback)
-#set(SELF_SRCS CallbackSet.cpp)
-
-xo_add_headeronly_library(${SELF_LIB})
-xo_install_library4(${SELF_LIB} ${PROJECT_NAME}Targets)
-
-# ----------------------------------------------------------------
-# external dependencies:
-
-#xo_dependency(${SELF_LIB} refcnt)
-
-# end CMakeLists.txt
diff --git a/.xo-callback/src/callback/CallbackSet.cpp b/.xo-callback/src/callback/CallbackSet.cpp
deleted file mode 100644
index 1a889f3a..00000000
--- a/.xo-callback/src/callback/CallbackSet.cpp
+++ /dev/null
@@ -1,13 +0,0 @@
-/* file CallbackSet.cpp
- *
- * author: Roland Conybeare, Sep 2022
- */
-
-#include "CallbackSet.hpp"
-
-namespace xo {
-    namespace fn {
-    } /*namespace fn*/
-} /*namespace xo*/
-
-/* end CallbackSet.cpp */
diff --git a/xo-callback/cmake/callbackConfig.cmake.in b/xo-callback/cmake/callbackConfig.cmake.in
index f7176f38..d6c98d89 100644
--- a/xo-callback/cmake/callbackConfig.cmake.in
+++ b/xo-callback/cmake/callbackConfig.cmake.in
@@ -3,4 +3,5 @@
 include(CMakeFindDependencyMacro)
 find_dependency(refcnt)
 include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
+include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Share.cmake")
 check_required_components("@PROJECT_NAME@")
diff --git a/xo-callback/cmake/xo-bootstrap-macros.cmake b/xo-callback/cmake/xo-bootstrap-macros.cmake
index aba31169..592272c0 100644
--- a/xo-callback/cmake/xo-bootstrap-macros.cmake
+++ b/xo-callback/cmake/xo-bootstrap-macros.cmake
@@ -19,7 +19,13 @@ endif()
 
 message(STATUS "XO_CMAKE_CONFIG_EXECUTABLE=${XO_CMAKE_CONFIG_EXECUTABLE}")
 
-if (NOT XO_SUBMODULE_BUILD)
+if (XO_SUBMODULE_BUILD)
+    if (("${CMAKE_MODULE_PATH}" STREQUAL "") OR ("${CMAKE_MODULE_PATH}" STREQUAL prefix))
+        # local version of xo-cmake macros
+        set(CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/xo-cmake/cmake")
+        message(STATUS "CMAKE_MODULE_PATH=${CMAKE_MODULE_PATH}")
+    endif()
+else()
     if (("${CMAKE_MODULE_PATH}" STREQUAL "") OR ("${CMAKE_MODULE_PATH}" STREQUAL prefix))
         # default to typical install location for xo-project-macros
         execute_process(COMMAND ${XO_CMAKE_CONFIG_EXECUTABLE} --cmake-module-path OUTPUT_VARIABLE CMAKE_MODULE_PATH)
diff --git a/xo-callback/include/xo/callback/CallbackSet.hpp b/xo-callback/include/xo/callback/CallbackSet.hpp
index cfc3047b..15e938be 100644
--- a/xo-callback/include/xo/callback/CallbackSet.hpp
+++ b/xo-callback/include/xo/callback/CallbackSet.hpp
@@ -1,290 +1,13 @@
+// TOOD: rename to RpCallbackSet
+
 /* @file CallbackSet.hpp */
 
 #pragma once
 
-//#include "indentlog/scope.hpp"
-//#include "indentlog/print/tag.hpp"
-#include <functional>
-#include <vector>
-#include <cstdint>
+#include "CallbackSetImpl.hpp"
 
 namespace xo {
     namespace fn {
-        /* identifies a particular callback in a CallbackSet (see below).
-         * an unique id is created:
-         *   CallbackSetImpl cbset = ...;
-         *   CallbackId cb_id = cbset.add_callback(..);
-         *
-         * can use id to remove callback later:
-         *   cbset.remove_callback(cb_id);
-         *
-         * Tag so xo-callback can be header-only
-         */
-        template <typename Tag>
-        class CallbackIdImpl {
-        public:
-            CallbackIdImpl() = default;
-            explicit CallbackIdImpl(uint32_t id) : id_{id} {}
-
-            /* generate a globally-unique id (not threadsafe) */
-            static CallbackIdImpl generate() {
-                static CallbackIdImpl s_last_id;
-
-                s_last_id = CallbackIdImpl(s_last_id.id() + 1);
-
-                return s_last_id;
-            } /*generate*/
-
-            uint32_t id() const { return id_; }
-
-        private:
-            uint32_t id_ = 0;
-        }; /*CallbackIdImpl*/
-
-        template <typename Tag>
-        inline bool operator==(CallbackIdImpl<Tag> lhs, CallbackIdImpl<Tag> rhs) { return lhs.id() == rhs.id(); }
-        template <typename Tag>
-        inline bool operator!=(CallbackIdImpl<Tag> lhs, CallbackIdImpl<Tag> rhs) { return lhs.id() != rhs.id(); }
-
-        using CallbackId = CallbackIdImpl<class CallbackId_tag>;
-
-        /*   queue add/remove callback instructions encountered during callback
-         *   execution, to avoid invalidating vector iterator.
-         *
-         */
-        template<typename Fn>
-        struct ReentrantCbsetCmd {
-            enum CbsetCmdEnum { AddCallback, RemoveCallback };
-
-            ReentrantCbsetCmd() = default;
-            ReentrantCbsetCmd(CbsetCmdEnum cmd, CallbackId id, Fn const & fn)
-                : cmd_{cmd}, id_{id}, fn_{fn} {}
-
-            static ReentrantCbsetCmd add(CallbackId id, Fn const & fn) {
-                return ReentrantCbsetCmd{AddCallback, id, fn};
-            } /*add*/
-
-            static ReentrantCbsetCmd remove(CallbackId id) {
-                return ReentrantCbsetCmd{RemoveCallback, id, Fn()};
-            } /*remove*/
-
-            bool is_add() const { return cmd_ == AddCallback; }
-            bool is_remove() const { return cmd_ == RemoveCallback; }
-            CallbackId id() const { return id_; }
-            Fn const & fn() const { return fn_; }
-
-        private:
-            /* AddCallback:    deferred CallbackSet<Fn>::add_callback(.fn)
-             * RemoveCallback: deferred CallbackSet<Fn>::remove_callback(.fn)
-             */
-            CbsetCmdEnum cmd_ = AddCallback;
-            /* operate on callback with this id */
-            CallbackId id_;
-            /* callback function to add/remove */
-            Fn fn_;
-        }; /*ReentrantCbsetCmd*/
-
-        /* record for remembering a single callback.
-         * callbacks are given unique ids so they can be removed later
-         */
-        template<typename Fn>
-        struct CbRecd {
-            CbRecd(CallbackId id, Fn const & fn) : id_{id}, fn_{fn} {}
-
-            CallbackId id_;
-            Fn fn_;
-        }; /*CbRecd*/
-
-        /* If Fnptr is a type such that this works:
-         *   Fnptr fn = ...;
-         *   using Fn = Fnptr::element_type;
-         *   Fn * native_fn = fn.get();
-         *   (native_fn->*member_fn)(args ...);
-         *
-         * then
-         *   CallbackSet<Fnptr> cbset = ...;
-         *   cbset.invoke(&Fn::member_fn, args...)
-         *
-         * calls
-         *   (cb->*member_fn)(args...)
-         *
-         * for each callback cb in this set.
-         *
-         * In addition,  calls hook methods:
-         *   cb->notify_add_callback()
-         *   cb->notify_remove_callback()
-         * when adding/removing callback.
-         *
-         * Require:
-         * - Fnptr::element_type
-         * - Fnptr::get() -> Fnptr::element_type const *
-         * - can invoke (Fnptr->*member_fn)(...)
-         *
-         * implementation is reentrant: running callbacks can safely make
-         * add/remove calls on the cbset that invoked them.
-         *
-         * not threadsafe.
-         */
-        template<typename Fn>
-        class CallbackSetImpl {
-        public:
-            using callback_type = typename Fn::element_type;
-            //using scope = xo::scope;
-
-        public:
-            CallbackSetImpl() = default;
-
-            /* support for range iterators */
-            typename std::vector<CbRecd<Fn>>::const_iterator begin() const { return cb_v_.begin(); }
-            typename std::vector<CbRecd<Fn>>::const_iterator end() const { return cb_v_.end(); }
-
-            /* invoke callbacks registered with this callback set */
-            template<typename ... Tn, typename ... Sn>
-            void invoke(void (callback_type::* member_fn)(Sn... args), Tn&&... args) {
-                this->cb_running_ = true;
-
-                try {
-                    for(CbRecd<Fn> const & cb_recd : this->cb_v_) {
-                        callback_type * native_cb = cb_recd.fn_.get();
-
-                        /* clang11 doesn't like (with cb=cb_recd.fn_)
-                         *   cb->*member_fn
-                         * when cb-> is overloaded
-                         */
-                        (native_cb->*member_fn)(args...);
-                    }
-
-                    this->make_deferred_changes();
-                } catch(...) {
-                    this->make_deferred_changes();
-                    throw;
-                }
-            } /*operator()*/
-
-            /* call fn(cb) for each callback present in this set */
-            void visit_callbacks(std::function<void (Fn const &)> fn) const {
-                CallbackSetImpl * self = const_cast<CallbackSetImpl *>(this);
-
-                self->cb_running_ = true;
-
-                try {
-                    for(Fn const & cb : this->cb_v_)
-                        fn(cb);
-
-                    this->make_deferred_changes();
-                } catch(...) {
-                    this->make_deferred_changes();
-                    throw;
-                }
-            } /*visit_callbacks*/
-
-            /* add callback target_fn to this callback set.
-             * reentrant
-             */
-            CallbackId add_callback(Fn const & target_fn) {
-                CallbackId id = CallbackId::generate();
-
-                if(this->cb_running_) {
-                    /* defer until callback execution completes */
-                    this->reentrant_cmd_v_.push_back(ReentrantCbsetCmd<Fn>::add(id, target_fn));
-                } else {
-#ifdef NOT_USING
-                    constexpr bool c_debug_enabled_flag = false;
-                    scope lscope(reflect::type_name<CallbackSetImpl>(),
-                                 "::add_callback", c_debug_enabled_flag);
-
-                    if (c_debug_enabled_flag) {
-                        lscope.log("before appending .cb_v[]",
-                                   xo::xtag("target_fn", (void*)target_fn.get()),
-                                   xo::xtag("target_fn.refcnt",
-                                            target_fn->reference_counter()));
-                    }
-#endif
-
-                    this->cb_v_.push_back(CbRecd(id, target_fn));
-
-#ifdef NOT_USING
-                    if (c_debug_enabled_flag) {
-                        lscope.log("after appending .cb_v[]",
-                                   xo::xtag("target_fn", (void *)target_fn.get()),
-                                   xo::xtag("target_fn.refcnt",
-                                            target_fn->reference_counter()));
-                    }
-#endif
-                }
-
-                return id;
-            } /*add_callback*/
-
-            void remove_callback(CallbackId id) {
-                if(this->cb_running_) {
-                    /* defer until callback execution completes */
-                    this->reentrant_cmd_v_.push_back(ReentrantCbsetCmd<Fn>::remove(id));
-                } else {
-                    this->remove_callback_impl(id);
-                }
-
-            } /*remove_callback*/
-
-#ifdef NOT_USING
-            /* remove callback target_fn from this callback set.
-             * noop if callback is not present
-             */
-            void remove_callback(Fn const & target_fn) {
-                if(this->cb_running_) {
-                    /* defer until callback execution completes */
-                    this->reentrant_cmd_v_.push_back(ReentrantCbsetCmd<Fn>::remove(target_fn));
-                } else {
-                    this->remove_callback_impl(target_fn);
-                }
-            } /*remove_callback*/
-#endif
-
-        private:
-            /* apply deferred changes to .cb_v[] */
-            void make_deferred_changes() {
-                this->cb_running_ = false;
-
-                std::vector<ReentrantCbsetCmd<Fn>> cmd_v;
-                std::swap(cmd_v, this->reentrant_cmd_v_);
-
-                for(ReentrantCbsetCmd<Fn> const & cmd : cmd_v) {
-                    if(cmd.is_add()) {
-                        this->cb_v_.push_back(CbRecd(cmd.id(), cmd.fn()));
-
-                        cmd.fn()->notify_add_callback();
-                    } else if(cmd.is_remove()) {
-                        this->remove_callback_impl(cmd.id());
-                    }
-                }
-            } /*make_deferred_changes*/
-
-            void remove_callback_impl(CallbackId target_id) {
-                for (auto ix = this->cb_v_.begin(); ix != this->cb_v_.end(); ++ix) {
-                    if (ix->id_ == target_id) {
-                        Fn target_fn = ix->fn_;
-
-                        this->cb_v_.erase(ix);
-
-                        target_fn->notify_remove_callback();
-                        break;
-                    }
-                }
-            } /*remove_callback_impl*/
-
-        private:
-            bool cb_running_ = false;
-            /* collection of callback functions */
-            std::vector<CbRecd<Fn>> cb_v_;
-            /* when a callback registered with *this, while running,
-             * attempts to add/remove a callback to/from this set
-             * (including removing itself),
-             * must defer until all callbacks have executed.
-             * remember deferred instructions here.
-             */
-            std::vector<ReentrantCbsetCmd<Fn>> reentrant_cmd_v_;
-        }; /*CallbackSetImpl*/
-
         template<typename NativeFn>
         using RpCallbackSet = CallbackSetImpl<rp<NativeFn>>;
 
@@ -300,18 +23,19 @@ namespace xo {
             template<typename ... Tn>
             void operator()(Tn&&... args) {
                 this->invoke(this->privileged_member_fn_, args...);
-            } /*operator()*/
+            }
 
         private:
-            /* implements NotifyCallbackSet's operator()(...) */
+            /** implements NotifyCallbackSet's operator()(...) **/
             MemberFn privileged_member_fn_;
-        }; /*NotifyCallbackSet*/
+        };
 
         template<typename NativeFn, typename Sret, typename ... Sn>
         inline NotifyCallbackSet<NativeFn, Sret (NativeFn::*)(Sn...)>
         make_notify_cbset(Sret (NativeFn::* member_fn)(Sn...)) {
             return NotifyCallbackSet<NativeFn, Sret (NativeFn::*)(Sn...)>(member_fn);
         } /*make_notify_cbset*/
+
     } /*namespace fn*/
 } /*namespace xo*/
 
diff --git a/.xo-callback/include/xo/callback/CallbackSetImpl.hpp b/xo-callback/include/xo/callback/CallbackSetImpl.hpp
similarity index 100%
rename from .xo-callback/include/xo/callback/CallbackSetImpl.hpp
rename to xo-callback/include/xo/callback/CallbackSetImpl.hpp
diff --git a/.xo-callback/include/xo/callback/UpCallbackSet.hpp b/xo-callback/include/xo/callback/UpCallbackSet.hpp
similarity index 100%
rename from .xo-callback/include/xo/callback/UpCallbackSet.hpp
rename to xo-callback/include/xo/callback/UpCallbackSet.hpp
diff --git a/.xo-callback/include/xo/callback/callback_concept.hpp b/xo-callback/include/xo/callback/callback_concept.hpp
similarity index 100%
rename from .xo-callback/include/xo/callback/callback_concept.hpp
rename to xo-callback/include/xo/callback/callback_concept.hpp