|As You can see dump_arr is a function - not a class method.|
The class itself sorts arrays, but does not dump them as HTML, so there is no reason this function to be located in the class file.
The only place dump_arr function is mentioned is in the example.php file and the function is located right there, in example.php file.
BTW CTRL+F keystroke will open the search tool in nearly any text editor. Then You type the search term - in this case the string dump_arr and press enter. The whole operation takes much less time than asking in a forum...