Review suggestions for GHC-02550

Author: Bodigrim

message-index/messages/GHC-02550/index.md

@@ -2,10 +2,11 @@
 title: Quantified predicate must have a class or type variable head
 summary: The head of a quantified constraint must be either a class or a type variable
 severity: error
-introduced: 9.4.1
+introduced: 9.6.1
 ---
 
-Quantified constraints are constraints which have their own constraints. The
+[Quantified constraints](https://downloads.haskell.org/ghc/9.12.1/docs/users_guide/exts/quantified_constraints.html)
+are constraints which have their own constraints. The
 *head* of a quantified constraint is the constraint on the right side of the
 `=>` operator. For example, the head of the quantified constraint `Ord a => Eq
 a` is `Eq a`. This error message states that the head of a quantified constraint