Modify rule S1206: "equals(Object obj)" and "hashCode()" should be overridden in pairs (hash_and_equals)

rules/S1206/dart/rule.adoc

@@ -1,15 +1,23 @@
 == Why is this an issue?
 
-In Dart, you must override either both or neither of the operator `==` and `hashCode()` method in order to keep the contract between the two:
+In Dart, you must override either both or neither of the operator `==` and the `hashCode()` method.
 
-- Whenever the `hashCode` method is invoked on the same object more than once, it must consistently return the same integer, provided no information used in `==` comparisons on the object is modified.
-- If two objects are equal according to the `==` operator, then calling the `hashCode` method on each of the two objects must produce the same integer result.
+That is required to keep the contract between the two:
+
+* whenever the `hashCode` method is invoked on the same object more than once, it must consistently return the same integer, provided no information used in `==` comparisons on the object is modified
+* if two objects are equal according to the `==` operator, then calling the `hashCode` method on each of the two objects must produce the same integer result
 
 By overriding only one of the two methods with a non-trivial implementation, this contract is almost certainly broken.
 
+=== Exceptions
+
+The rule does not raise in mixins, because they are not supposed to be instantiated directly, but rather included in other classes.
+
+The rule raises, however, on mixin classes, since they can also be used as normal classes, and instantiated directly.
+
 === Noncompliant code example
 
-[source,dart]
+[source,dart,diff-id=1,diff-type=noncompliant]
 ----
 class A {
   final int value;
@@ -22,7 +30,7 @@ class A {
 
 === Compliant solution
 
-[source,dart]
+[source,dart,diff-id=1,diff-type=compliant]
 ----
 class A {
   final int value;
@@ -38,4 +46,28 @@ class A {
 
 == Resources
 
-* https://dart.dev/tools/linter-rules/unnecessary_overrides[Dart Lint rule]
+* Dart Docs - https://dart.dev/tools/linter-rules/hash_and_equals[Dart Linter rule - hash_and_equals]
+* Dart Docs - https://dart.dev/language/mixins[Language - Classes & objects - Mixins]
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+=== Message
+
+* Missing a corresponding override of 'hashCode'.
+* Missing a corresponding override of '=='.
+
+=== Highlighting
+
+The identifier of the overridden method: either `==` or `hashCode`.
+
+'''
+== Comments And Links
+(visible only on this page)
+
+include::../comments-and-links.adoc[]
+
+endif::env-github,rspecator-view[]