[Plugin: MailChimp List Subscribe Form] How to display the input value?

I’d like to get the value=”enter email address” to display within the input box on the front end.

I’ve amended line 102 of mailchimp_widget.php to add a value e.g.

<input type="text" size="18" value="enter email address" name="<?php echo esc_attr($opt); ?>" id="<?php echo esc_attr($opt); ?>" class="mc_input"/>

However, although the text ‘enter email address’ is there in the source code I can’t see it in the front end. What do I need to tweak to make it display?

EDIT: Don’t know why but by setting .mc_var_EMAIL to display: none is CSS the value displays??