--- a/STYLE.md	Tue Aug 14 11:23:32 2018 +0200
+++ b/STYLE.md	Thu Oct 18 21:21:00 2018 +0200
@@ -1,13 +1,53 @@
 PROJECT NAME CODING STYLE
 =========================
 
-General
-=======
+File content
+============
 
-- Always use 4 spaces as indentation (expect Makefiles),
 - Use UTF-8 charset,
 - Use Unix line endings,
-- Never write two blank consecutives blank lines,
+- Never write two blank consecutives blank lines.
+
+Indent
+======
+
+Use tabs to indent and spaces for alignment. Tabs are meant and designed for
+indenting code and have the advantage of being configurable. On the other hand
+to keep code clean, you must align content with spaces only *within* a line.
+
+Note: we recommend 8 columns to avoid high number of indentations.
+
+Example (show whitespace in your editor)
+
+```cpp
+class foo {
+public:
+	enum type {
+		dummy_value,            // dummy comment
+		other_value             // other comment
+	};
+
+	void long_function_name(very_long_type x1,
+	                        very_long_type x2)
+	{
+		const map<string, string> m{
+			{ "hostname",   "127.0.0.1"     },
+			{ "port",       "6667"          }
+		};
+	}
+};
+```
+
+As a rule of thumb, tabs must always be all length.
+
+Example of incorrect usage:
+
+```cpp
+	{ "hostname",	"127.0.0.1"	},
+	{ "port",	"6667"		}
+```
+
+This example will not align correctly if tabstops are not set to 8.
 
 C++
 ===
@@ -15,8 +55,8 @@
 Style
 -----
 
-- Do not exceed 120 characters for lines of code,
-- Do not exceed 80 characters for comments,
+- Do not exceed 120 columns for lines of code,
+- Do not exceed 80 columns for comments,
 
 ### Braces
 
@@ -27,17 +67,17 @@
 
 ```cpp
 if (condition) {
-    apply();
-    add();
+	apply();
+	add();
 } else
-    ok();
+	ok();
 
 if (condition)
-    validate();
+	validate();
 
 if (foo)
-    state = long + conditional + that + requires + several + lines +
-            to + complete;
+	state = long + conditional + that + requires + several + lines +
+	        to + complete;
 ```
 
 Functions require braces on their own lines.
@@ -52,7 +92,7 @@
 
 ```cpp
 sort([&] (auto&) {
-    return true;
+	return true;
 });
 ```
 
@@ -65,7 +105,7 @@
 
 ```cpp
 if (foo)
-    destroy(sizeof (int));
+	destroy(sizeof (int));
 ```
 
 ### References and pointers
@@ -99,23 +139,23 @@
 
 ```cpp
 #if defined(FOO)
-#   include <foo.hpp>
+#	include <foo.hpp>
 #endif
 
 namespace baz {
 
 class object {
 private:
-    std::string name_;
+	std::string name_;
 
 public:
-    auto name() const noexcept -> const std::string&;
+	auto name() const noexcept -> const std::string&;
 };
 
 template <typename Archive>
 void open(const Archive& ar)
 {
-    bool is_valid = false;
+	bool is_valid = false;
 }
 
 } // !baz
@@ -143,9 +183,9 @@
 
 ```cpp
 enum class color {
-    blue,
-    red,
-    green
+	blue,
+	red,
+	green
 };
 ```
 
@@ -157,10 +197,10 @@
 ```cpp
 switch (variable) {
 case foo:
-    do_some_stuff();
-    break;
+	do_some_stuff();
+	break;
 default:
-    break;
+	break;
 }
 ```
 
@@ -188,7 +228,7 @@
 
 ```cpp
 #if 0
-    broken_stuff();
+	broken_stuff();
 #endif
 ```
 
@@ -219,7 +259,7 @@
 
 ### C language
 
-Do not use old C stuff like `void *`, `srand/rand`, `printf` or anything that
+Do not use old C stuff like `void*`, `srand/rand`, `printf` or anything that
 can be rewritten in modern C++.
 
 ### RTTI
@@ -243,10 +283,10 @@
 ```cpp
 auto clean(std::string input) -> std::string
 {
-    if (!input.empty() && input.back() == '\r')
-        input.pop_back();
+	if (!input.empty() && input.back() == '\r')
+		input.pop_back();
 
-    return input;
+	return input;
 }
 ```
 
@@ -263,9 +303,9 @@
 ```cpp
 auto operator[](unsigned index) -> T&
 {
-    assert(index < length_);
+	assert(index < length_);
 
-    return data_[index];
+	return data_[index];
 }
 ```
 
@@ -304,7 +344,7 @@
 ```cpp
 namespace util {
 
-auto clean(std::string input) -> std::string
+auto clean(std::string input) -> std::string;
 
 } // !util
 ```
@@ -325,9 +365,9 @@
 ```cpp
 std::vector<int> v{1, 2, 3};
 
-foo({1, 2});                    // type deduced
+foo({1, 2});					// type deduced
 
-return { "true", false };       // std::pair returned
+return { "true", false };	   // std::pair returned
 ```
 
 Use the assignment for primitive types:
@@ -350,16 +390,16 @@
 ```cpp
 class foo {
 public:
-    enum class type {
-        a,
-        b
-    };
+	enum class type {
+		a,
+		b
+	};
 
 private:
-    int member_{0};
+	int member_{0};
 
 public:
-    void some_function();
+	void some_function();
 };
 ```
 
@@ -370,18 +410,18 @@
 
 ```cpp
 struct point {
-    int x{0};
-    int y{0};
+	int x{0};
+	int y{0};
 };
 
 template <>
 struct info_traits<point> {
-    template <typename Archive>
-    static void serialize(Archive& ar, const point& point)
-    {
-        ar.write(point.x);
-        ar.write(point.y);
-    }
+	template <typename Archive>
+	static void serialize(Archive& ar, const point& point)
+	{
+		ar.write(point.x);
+		ar.write(point.y);
+	}
 };
 ```
 
@@ -394,9 +434,9 @@
 
 ```cpp
 if (a_condition_is_not_valid)
-    return nullptr;
+	return nullptr;
 if (an_other_condition)
-    return nullptr;
+	return nullptr;
 
 auto x = std::make_shared<object>();
 
@@ -418,11 +458,11 @@
 
 ```cpp
 auto it = std::find_if(v.begin(), v.end(), [&] (const auto& obj) {
-    return obj.key() == "foo";
+	return obj.key() == "foo";
 });
 
 for (const auto& pair : a_map)
-    std::cout << pair.first << " = " << pair.second << std::endl;
+	std::cout << pair.first << " = " << pair.second << std::endl;
 ```
 
 But do not use `auto` to write code like in python, this is not acceptable:
@@ -441,7 +481,7 @@
 
 void load(std::string_view id, std::string_view path)
 {
-    std::cout << "loading: " << id << " from path: " << path << std::endl;
+	std::cout << "loading: " << id << " from path: " << path << std::endl;
 }
 ```
 
@@ -453,10 +493,10 @@
 ```cpp
 auto find(std::string_view id) -> std::optional<int>
 {
-    if (auto it = foo.find(id); it != foo.end())
-        return it->second;
+	if (auto it = foo.find(id); it != foo.end())
+		return it->second;
 
-    return std::nullopt;
+	return std::nullopt;
 }
 ```
 
@@ -482,11 +522,11 @@
 
 ```cmake
 foreach (c ${COMPONENTS})
-    string(TOUPPER ${c} CMP)
+	string(TOUPPER ${c} CMP)
 
-    if (${WITH_${CMP}})
-        add_executable(${c} ${c}.cpp)
-    endif ()
+	if (${WITH_${CMP}})
+		add_executable(${c} ${c}.cpp)
+	endif ()
 endforeach ()
 ```
 
@@ -497,20 +537,20 @@
 
 ```cmake
 set(
-    FILES
-    ${myapp_SOURCE_DIR}/main.cpp
-    ${myapp_SOURCE_DIR}/foo.cpp
-    ${myapp_SOURCE_DIR}/bar.cpp
+	FILES
+	${myapp_SOURCE_DIR}/main.cpp
+	${myapp_SOURCE_DIR}/foo.cpp
+	${myapp_SOURCE_DIR}/bar.cpp
 )
 
 command_with_lot_of_arguments(
-    TARGET foo
-    INSTALL On
-    SOURCES
-        ${myapp_SOURCE_DIR}/main.cpp
-        ${myapp_SOURCE_DIR}/foo.cpp
-        ${myapp_SOURCE_DIR}/bar.cpp
-    COMMENT "Some comment"
+	TARGET foo
+	INSTALL On
+	SOURCES
+		${myapp_SOURCE_DIR}/main.cpp
+		${myapp_SOURCE_DIR}/foo.cpp
+		${myapp_SOURCE_DIR}/bar.cpp
+	COMMENT "Some comment"
 ```
 
 Modern CMake
@@ -539,9 +579,9 @@
 
 ```cmake
 target_link_libraries(
-    myapp
-    $<$<STREQUAL:${CMAKE_SYSTEM_NAME},Windows>:shlwapi>
-    $<$<STREQUAL:${CMAKE_SYSTEM_NAME},Linux>:dl>
+	myapp
+	$<$<STREQUAL:${CMAKE_SYSTEM_NAME},Windows>:shlwapi>
+	$<$<STREQUAL:${CMAKE_SYSTEM_NAME},Linux>:dl>
 ```
 
 Warning: do never test against `CMAKE_BUILD_TYPE` in any CMakeLists.txt, IDEs
@@ -562,10 +602,10 @@
 
 ```cmake
 target_include_directories(
-    mylib
-    PUBLIC
-        $<BUILD_INTERFACE:${mylib_SOURCE_DIR}>
-        $<INSTALL_INTERFACE:include>
+	mylib
+	PUBLIC
+		$<BUILD_INTERFACE:${mylib_SOURCE_DIR}>
+		$<INSTALL_INTERFACE:include>
 )
 target_link_libraries(mylib foo)
 ```
@@ -580,10 +620,10 @@
 
 ```cmake
 set(
-    FILES
-    ${myapp_SOURCE_DIR}/main.cpp
-    ${myapp_SOURCE_DIR}/a.cpp
-    ${myapp_SOURCE_DIR}/b.cpp
+	FILES
+	${myapp_SOURCE_DIR}/main.cpp
+	${myapp_SOURCE_DIR}/a.cpp
+	${myapp_SOURCE_DIR}/b.cpp
 )
 
 add_executable(myapp ${FILES})
@@ -636,14 +676,14 @@
 You can use three backticks and the language specifier or just indent a block by
 for leading spaces if you don't need syntax.
 
-    ```cpp
-    std::cout << "hello world" << std::endl;
-    ```
+	```cpp
+	std::cout << "hello world" << std::endl;
+	```
 
 And without syntax:
 
 ```markdown
-    This is simple code block.
+	This is simple code block.
 ```
 
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