Safari HTML5 textarea support

I designed a web using HTML5 tag:

<textarea name="comments6" maxlength="500" cols="50" rows="8" required></textarea>

The text area is "required" to contain input text. However, Safari for both Mac and iOS ignore the "required" field.

It worked on Google Chrome, Microsoft IE10, and FIrefox browsers.

Please refer to my web below:

http://survey.writeabort.com/

if you click on "Submit" when any of the text area has no input text, the browser should show "Please fill out this fill"