CPP-4873 S1001: Literals namespaces should be allowlisted from the rule

rules/S1001/cfamily/rule.adoc

@@ -2,8 +2,11 @@
 
 `using` directives add additional scopes to the set of scopes searched during name lookup. All identifiers in these scopes become visible, increasing the possibility that the identifier found by the compiler does not meet developer expectations.
 
-Using-declarations or fully-qualified names restricts the set of names considered to only the name explicitly specified, and so these are safer options.
+_Using-declarations_ or fully-qualified names restricts the set of names considered to only the name explicitly specified, and so these are safer options.
 
+=== Exceptions
+
+It is not easy to fully qualify the content of the `std::literals` and `std::placeholders` namespaces. Therefore, this rule does not raise violations for `using` directives that target these namespaces or their sub-namespaces.
 
 === Noncompliant code example