Add explanation to docs

Author: odersky

docs/docs/reference/other-new-features/indentation.md

@@ -69,7 +69,8 @@ or
 Colons at the end of lines are their own token, distinct from normal `:`.
 The Scala grammar is changed so that colons at end of lines are accepted at all points
 where an opening brace is legal, except if the previous token can already start an
-indentation region.
+indentation region. Special provisions are taken so that method result types can still use a colon on
+the end of a line, followed by the actual type on the next.
 
 ### Special Treatment of Case Clauses
 
@@ -93,7 +94,6 @@ case 5 => print("V")
 println(".")
 ```
 
-
 ### The End Marker
 
 Indentation-based syntax has many advantages over other conventions. But one possible problem is that it makes it hard to discern when a large indentation region ends, since there is no specific token that delineates the end. Braces are not much better since a brace by itself also contains no information about what region is closed.
@@ -148,14 +148,16 @@ enum IndentWidth:
     def < (that: IndentWidth): Boolean = this <= that && !(that <= this)
 
     override def toString: String =
-        def kind(ch: Char) = ch match
-            case ' ' => "space"
-            case '\t' => "tab"
-            case _ => s"'$ch'-character"
-
         this match
-        case Run(ch, n) => s"$n ${kind(ch)}${if (n == 1) "" else "s"}"
-        case Conc(l, r) => s"$l, $r"
+        case Run(ch, n) =>
+            val kind = ch match
+                case ' '  => "space"
+                case '\t' => "tab"
+                case _    => s"'$ch'-character"
+            val suffix = if n == 1 then "" else "s"
+            s"$n $kind$suffix"
+        case Conc(l, r) =>
+          s"$l, $r"
 
 object IndentWidth:
     private inline val MaxCached = 40