Polish docs

Author: odersky

compiler/src/dotty/tools/dotc/transform/ExpandPrivate.scala

@@ -44,7 +44,7 @@ class ExpandPrivate extends MiniPhaseTransform with IdentityDenotTransformer { t
   // This phase moves methods around (in infotransform) so it may need to make other methods public
   override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[MoveStatics])
 
-  override def changesMembers = true
+  override def changesMembers = true // the phase introduces new members with mangled names
 
   override def checkPostCondition(tree: Tree)(implicit ctx: Context): Unit = {
     tree match {

compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala

@@ -49,7 +49,7 @@ class ExtensionMethods extends MiniPhaseTransform with DenotTransformer with Ful
 
   override def runsAfterGroupsOf = Set(classOf[FirstTransform]) // need companion objects to exist
 
-  override def changesMembers = true // the pahse adds extension methods
+  override def changesMembers = true // the phase adds extension methods
 
   override def transform(ref: SingleDenotation)(implicit ctx: Context): SingleDenotation = ref match {
     case moduleClassSym: ClassDenotation if moduleClassSym is ModuleClass =>

compiler/src/dotty/tools/dotc/transform/RestoreScopes.scala

@@ -22,7 +22,7 @@ class RestoreScopes extends MiniPhaseTransform with IdentityDenotTransformer { t
   import ast.tpd._
   override def phaseName = "restoreScopes"
 
-  override def changesMembers = true
+  override def changesMembers = true // the phase affects scopes, applying tree transformations of previous phases
 
   /* Note: We need to wait until we see a package definition because
    * DropEmptyConstructors changes template members when analyzing the