With MentaAjax 2.0 you dont need to write a callback function for innerHTML operations. It gets the string "stringHere" after "innerHTML" specified on the innerAction as the id of html element to place the response.
r.setUrl("TestAction.innerHTMLstringHere.mtw");
innerHTML: Says to MentaAjax that you can place the response with html code in any container.
stringHere: It is the id of container that MentaAjax will place the html code.