anchor.diff:      // those first.
       var lineStart =
           findLineStart(_span.context, _span.text, _span.start.column);
  -    assert(lineStart != null); // enfoced by [new Highlighter]
  +    assert(lineStart != null); // enforced by [new Highlighter]
   
       var context = _span.context;
       if (lineStart > 0) {
  
positive.code:   ///
    /// This method should only be called once.
    String highlight() {
      //if (_span.length == 0 && _span.context.isEmpty) return "";
  
      _writeSidebar(end: glyph.downEnd);
      _buffer.writeln();
  
  
negative.code:     if (lines.last.isEmpty && lines.length > 1) lines.removeLast();
  
      _writeFirstLine(lines.first);
      var lastLineIndex = _span.end.line - _span.start.line;
      if (_multiline) {
        _writeIntermediateLines(
            lines.skip(1).take(lastLineIndex - 1));
        _writeLastLine(lines[lastLineIndex]);
      }
      _writeTrailingLines(lines.skip(lastLineIndex + 1));
  
      _writeSidebar(end: glyph.upEnd);
  
  