diff --git a/toml/region.hpp b/toml/region.hpp
index db830c7..54d9106 100644
--- a/toml/region.hpp
+++ b/toml/region.hpp
@@ -15,7 +15,7 @@ namespace toml
 namespace detail
 {
 
-// helper function to avoid std::string(0, 'c')
+// helper function to avoid std::string(0, 'c') or std::string(iter, iter)
 template<typename Iterator>
 std::string make_string(Iterator first, Iterator last)
 {
@@ -28,9 +28,7 @@ inline std::string make_string(std::size_t len, char c)
     return std::string(len, c);
 }
 
-// region in a container, normally in a file content.
-// shared_ptr points the resource that the iter points.
-// combinators returns this.
+// region_base is a base class of location and region that are defined below.
 // it will be used to generate better error messages.
 struct region_base
 {
@@ -48,16 +46,19 @@ struct region_base
     virtual std::string line()     const {return std::string("unknown line");}
     virtual std::string line_num() const {return std::string("?");}
 
-    virtual std::size_t before()   const noexcept {return 0;}
+    // length of the region
     virtual std::size_t size()     const noexcept {return 0;}
+    // number of characters in the line before the region
+    virtual std::size_t before()   const noexcept {return 0;}
+    // number of characters in the line after the region
     virtual std::size_t after()    const noexcept {return 0;}
 };
 
-// location in a container, normally in a file content.
-// shared_ptr points the resource that the iter points.
-// it can be used not only for resource handling, but also error message.
-//
+// location represents a position in a container, which contains a file content.
 // it can be considered as a region that contains only one character.
+//
+// it contains pointer to the file content and iterator that points the current
+// location.
 template<typename Container>
 struct location final : public region_base
 {
@@ -131,6 +132,10 @@ struct location final : public region_base
     const_iterator iter_;
 };
 
+// region represents a range in a container, which contains a file content.
+//
+// it contains pointer to the file content and iterator that points the first
+// and last location.
 template<typename Container>
 struct region final : public region_base
 {
diff --git a/toml/value.hpp b/toml/value.hpp
index 739f676..340396f 100644
--- a/toml/value.hpp
+++ b/toml/value.hpp
@@ -474,7 +474,7 @@ class value
           region_info_(std::make_shared<region_base>(region_base{}))
     {
         array ary; ary.reserve(list.size());
-        for(auto& elem : list) {ary.emplace_back(std::move(elem));}
+        for(const auto& elem : list) {ary.emplace_back(elem);}
         assigner(this->array_, std::move(ary));
     }
     template<typename T, typename std::enable_if<detail::is_container<T>::value,
@@ -486,7 +486,7 @@ class value
         this->region_info_ = std::make_shared<region_base>(region_base{});
 
         array ary; ary.reserve(list.size());
-        for(auto& elem : list) {ary.emplace_back(std::move(elem));}
+        for(const auto& elem : list) {ary.emplace_back(elem);}
         assigner(this->array_, std::move(ary));
         return *this;
     }
@@ -930,7 +930,7 @@ visit(Visitor&& visitor, toml::value& v)
 }
 
 template<typename Visitor>
-detail::return_type_of_t<Visitor, toml::boolean&>
+detail::return_type_of_t<Visitor, toml::boolean&&>
 visit(Visitor&& visitor, toml::value&& v)
 {
     switch(v.type())