NL.11 literals

CppCoreGuidelines.md

@@ -18853,6 +18853,7 @@ Naming and layout rules:
 * [NL.8: Use a consistent naming style](#Rl-name)
 * [NL.9: Use `ALL_CAPS` for macro names only](#Rl-all-caps)
 * [NL.10: Avoid CamelCase](#Rl-camel)
+* [NL.11: Make literals readable](#Rl-literals)
 * [NL.15: Use spaces sparingly](#Rl-space)
 * [NL.16: Use a conventional class member declaration order](#Rl-order)
 * [NL.17: Use K&R-derived layout](#Rl-knr)
@@ -19160,6 +19161,38 @@ Some IDEs have their own opinions and add distracting space.
 
 We value well-placed whitespace as a significant help for readability. Just don't overdo it.
 
+### <a name="Rl-literals"></a>NL.11: Make literals readable
+
+##### Reason
+
+Readability.
+
+###### Example
+
+Use digit separators to avoid long strings of digits
+
+    auto c = 299'792'458; // m/s2
+    auto q2 = 0b0000'1111'0000'0000;
+    auto ss_number = 123'456'7890;
+
+###### Example
+
+Use literal suffixes where clarification is needed
+
+    auto hello = "Hello!"s; // a std::string
+    auto world = "world";   // a C-style string
+    auto interval = 100ms;  // using <chrono>
+
+###### Note
+
+Literals should not be springled all over the code as ["magic constants'](#Res-magic),
+but it is still a good idea to make them readable where they are defined.
+It is easy to make a yypo in a long string of integers.
+
+###### Enforcement
+
+Flag long digit sequences. The trouble is to define "long"; maybe 7.
+
 ### <a name="Rl-order"></a>NL.16: Use a conventional class member declaration order
 
 ##### Reason