Add more xrefs to carbon-language#2022 and to carbon-language#1084.

proposals/p2188.md

@@ -172,7 +172,10 @@ ignore part of a value.
 
 -   _binding-pattern_ ::= `_` `:` _expression_
 
-The behavior is equivalent to that of an `unused` binding with a unique name.
+See [#2022](https://github.com/carbon-language/carbon-lang/pull/2022) for
+details.
+
+The behavior is similar to that of an `unused` binding with a unique name.
 
 ```
 fn F(n: i32) {
@@ -185,6 +188,22 @@ fn F(n: i32) {
 }
 ```
 
+As specified in [#1084](p1084.md), function redeclarations may replace named
+bindings with wildcards but may not use different names.
+
+```
+fn G(n: i32);
+fn H(n: i32);
+fn J(n: i32);
+
+// ✅ Does not use `n`.
+fn G(_: i32) {}
+// ❌ Error: name of parameter does not match declaration.
+fn H(m: i32) {}
+// ✅ Does not use `n`.
+fn J(unused n: i32);
+```
+
 #### Generic bindings
 
 A `:!` can be used in place of `:` for a binding that is usable at compile time.