Update docs

Author: odersky

docs/docs/reference/changed-features/vararg-patterns.md

@@ -0,0 +1,40 @@
+---
+layout: doc-page
+title: "Vararg Splices"
+---
+
+The syntax of vararg splices in patterns and function arguments has changed. The new syntax uses a postfix `*`,  analogously to how a vararg parameter is declared.
+
+```scala
+val arr = Array(1, 2, 3)
+val lst = List(0, arr*)                  // vararg splice argument
+lst match
+   case List(0, 1, xs*) => println(xs)   // binds xs to Seq(2, 3)
+   case List(1, _*) =>                   // wildcard pattern
+```
+
+The old syntax for splice arguments will be phased out.
+
+```scala
+/*!*/ val lst = List(0, arr: _*)         // syntax error
+      lst match
+         case List(1, 2, xs @ _*)        // ok, equivalent to `xs*`
+```
+
+## Syntax
+
+```
+ArgumentPatterns  ::=  ‘(’ [Patterns] ‘)’
+                    |  ‘(’ [Patterns ‘,’] Pattern2 ‘*’ ‘)’
+
+ParArgumentExprs  ::=  ‘(’ [‘using’] ExprsInParens ‘)’
+                    |  ‘(’ [ExprsInParens ‘,’] PostfixExpr ‘*’ ‘)’
+```
+
+## Compatibility considerations
+
+To enable cross compilation between Scala 2 and Scala 3, the compiler will
+accept both the old and the new syntax. Under the `-source 3.1` setting, an error
+will be emitted when the old syntax is encountered.
+
+

docs/docs/reference/changed-features/vararg-splices.md

@@ -141,8 +141,8 @@ sidebar:
               url: docs/reference/changed-features/overload-resolution.html
             - title: Match Expressions
               url: docs/reference/changed-features/match-syntax.html
-            - title: Vararg Patterns
-              url: docs/reference/changed-features/vararg-patterns.html
+            - title: Vararg Splices
+              url: docs/reference/changed-features/vararg-splices.html
             - title: Pattern Bindings
               url: docs/reference/changed-features/pattern-bindings.html
             - title: Pattern Matching