anchor.diff:    /**
      * Clears the text content for each element in the current selection.
      */
  -  textNull() {
  +  void textNull() {
       each((node, data, i, j) {
         node.text = "";
       });
  
positive.code:    * element. The function's return value is then used to set each element's
     * text content. A null value will clear the content.
     */
    textFunc(final objectFunction fn) {
      each((node, data, i, j) {
        var v = fn(node, data, i, j);
        node.text = (v == null ? "" : v.toString());
  
negative.code:    * or remove. The values may be functions that are evaluated for
     * each element.
     */
    void attrMap(final Map<String, Object> attrs) {
      attrs.forEach((final String name, final Object value) {
        if (value == null) {
          attrNull(name);
  