Modify Rule S1679: fix Dart example, add implementation details

rules/S1679/dart/rule.adoc

@@ -7,8 +7,8 @@ In such case it's recommended to use `rethrow` instead of just `throw`, to prese
 ----
 try {
   ...
-} catch (ex, stacktrace) {
-  rethrow ex;                // preserves the original exception with its stacktrace
+} catch (ex) {
+  rethrow;                // preserves the original exception with its stacktrace
 }
 ----
 
@@ -41,11 +41,30 @@ void foo() {
     methodThrowsException();
   } catch (ex) {
     // ...
-    rethrow ex;
+    rethrow;
   }
 }
 ----
 
 == Resources
 
-* https://dart.dev/tools/linter-rules/use_rethrow_when_possible[Dart Lint rule]
+* Dart Docs - https://dart.dev/tools/linter-rules/use_rethrow_when_possible[Dart Linter rule - use_rethrow_when_possible]
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+=== Message
+
+* Use 'rethrow' to rethrow a caught exception.
+
+=== Highlighting
+
+The `throw` statement with the argument.
+
+'''
+
+endif::env-github,rspecator-view[]
+