anchor.diff:  /// A widget that can be copied by a [Mimic].
   ///
   /// This widget's State, [MimicableState], contains an API for initiating the
  -/// mimic operation.
  +/// mimic operation. Typically you would obtain this state by assigning a
  +/// [GlobalKey] to the [Mimicable] and then using [GlobalKey.currentState].
   class Mimicable extends StatefulWidget {
     /// Creates a widget that can be copies by a [Mimic].
     Mimicable({ Key key, this.child }) : super(key: key);
  
positive.code:     return new MimicableHandle._(this);
    }
  
    /// Start the mimicking process and mimic this object in the
    /// enclosing [Overlay].
    ///
    /// The child of this object will no longer be built at this
    /// location in the tree. Instead, (1) this widget will build a
    /// transparent placeholder with the same dimensions as the widget
    /// had when the mimicking process started and (2) the child will be
    /// placed in the enclosing overlay.
    MimicOverlayEntry liftToOverlay() {
      OverlayState overlay = Overlay.of(context, debugRequiredFor: config);
      return new MimicOverlayEntry._(startMimic(), overlay);
  
negative.code: }
  
  /// An overlay entry that is mimicking another widget.
  ///
  /// Obtained from [MimicableState.liftToOverlay].
  class MimicOverlayEntry {
    MimicOverlayEntry._(this._handle, this._overlay) {
      _initialGlobalBounds = _handle.globalBounds;
  