code: public String getSample(int line, int column, Janitor janitor) {
          String sample = null;
          String text = source.getLine(line, janitor);
  
          if (text != null) {
              if (column > 0) {
                  String marker = Utilities.repeatString(" ", column - 1) + "^";
  
                  if (column > 40) {
                      int start = column - 30 - 1;
                      int end = (column + 10 > text.length() ? text.length() : column + 10 - 1);
                      sample = "   " + text.substring(start, end) + Utilities.eol() + "   " +
                              marker.substring(start, marker.length());
                  } else {
                      sample = "   " + text + Utilities.eol() + "   " + marker;
                  }
              } else {
                  sample = text;
              }
          }
  
          return sample;
      }
docs: Returns a sampling of the source at the specified line and column,
  of null if it is unavailable.