Document dotty internal Annotations

src/dotty/annotation/internal/Alias.scala

@@ -2,6 +2,9 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
+/** An annotation to record a Scala2 pickled alias.
+ *  @param aliased  A TermRef pointing to the aliased field.
+ */
 class Alias(aliased: Any) extends Annotation {
 
 }

src/dotty/annotation/internal/AnnotationDefault.scala

@@ -2,6 +2,7 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
+/** An annotation to tag Java annotation default values */
 class AnnotationDefault extends Annotation {
 
 }

src/dotty/annotation/internal/Child.scala

@@ -2,6 +2,5 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
-class Child[T] extends Annotation {
-
-}
+/** An annotation to indicate a child class or object of the annotated class. */
+class Child[T] extends Annotation

src/dotty/annotation/internal/Repeated.scala

@@ -2,4 +2,9 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
+/** An annotation produced by desugaring to indicate that a
+ *  sequence is a repeated parameter. I.e.
+ *
+ *      T*  is expanded by Desugar to    Seq[T] @Repeated
+ */
 final class Repeated() extends Annotation