code: public String getFragmentByLines(int startLine, int endLine) {
      Preconditions.checkArgument(startLine <= endLine);
      return Joiner.on("\n").join(getLines(startLine, endLine)) + "\n";
    }
docs: Returns a fragment of the source code between the two stated line numbers. The parameters
  represent <b>inclusive</b> line numbers.
  
  <p>The returned fragment will end in a newline.