docs: public void swapTwoChildren(GroovySourceAST t) {
          // this swaps the two child nodes, see javadoc above for explanation of implementation
          GroovySourceAST a = (GroovySourceAST) t.getFirstChild();
          GroovySourceAST b = (GroovySourceAST) a.getNextSibling();
  
          t.setFirstChild(b);
          a.setNextSibling(null);
          b.setNextSibling(a);
      }