The Placeholder character is a character used to represent the absence of user input in a RadMaskedInput control. The default value is an underscore. The Placeholder character will be displayed in a RadMaskedInput control for any mask position that the user has not filled in yet.
[XAML] Example 1: Using the default placeholder
<telerik:RadMaskedTextInput Mask="####" />
Figure 1 : Default placeholder
If you want to change the default Placeholder, you should set a RadMaskedInput control's Placeholder property, like in the example below:
[XAML] Example 1: Change the default placeholder
<telerik:RadMaskedTextInput Mask="####" Placeholder="$" />
Figure 2: Custom placeholder
You can set a watermark content to the RadMaskedInput controls by using the EmptyContent and EmptyContentTemplate properties. When the Value of a RadMaskedInput control is null or empty the EmptyContent will be displayed. For more information, read Watermark.