Adds the next chunk to this.
Adds the substring defined by start and end-exclusive to this.
If isLast is true closes this.
void addSlice(String str, int start, int end, bool isLast);
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dart.dev/stable/2.5.0/dart-convert/StringConversionSinkMixin/addSlice.html