anchor.diff:    /// The Flutter framework operates in logical pixels, so it is rarely
     /// necessary to directly deal with this property.
     ///
  +  /// When this changes, [onMetricsChanged] is called.
  +  ///
     /// See also:
     ///
     ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  
positive.code:   /// intrusions in the display (e.g. overscan regions on television screens or
    /// phone sensor housings).
    ///
    /// See also:
    ///
    ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  
negative.code: 
    /// The dimensions of the rectangle into which the application will be drawn,
    /// in physical pixels.
    ///
    /// When this changes, [onMetricsChanged] is called.
    ///
    /// At startup, the size of the application window may not be know before Dart
    /// code runs. If this value is observed early in the application lifecycle,
    /// it may report [Size.zero].
    ///
    /// This value does not take into account any on-screen keyboards or other
    /// system UI. The [padding] and [viewInsets] properties provide a view into
    /// how much of each side of the application may be obscured by system UI.
    ///
    /// See also:
    ///
  