promptChar - string (default: '_')

Designates the character used to represent the absence of user input in the widget.
Note that the promptChar should not be equal to any of the used mask literals in the mask value.

The code demonstrates different prompt char specification.

<input id="maskedtextbox" />
<script type="text/javascript">

jQuery(function($) {
             mask: "(00000)",
             promptChar: ' ' //specify prompt char as empty char