anchor.diff:      bool softWrap,
       TextOverflow overflow,
       int maxLines,
  -    Widget child
  +    @required Widget child,
     }) {
       assert(context != null);
       assert(child != null);
  
positive.code:   /// A const-constructible default text style that provides fallback values.
    ///
    /// Returned from [of] when the given [BuildContext] doesn't have an enclosing default text style.
    const DefaultTextStyle.fallback()
      : style = const TextStyle(),
        textAlign = null,
  
negative.code:     this.softWrap: true,
      this.overflow: TextOverflow.clip,
      this.maxLines,
      @required Widget child,
    }) : super(key: key, child: child) {
      assert(style != null);
      assert(softWrap != null);
  