Prompt character is the character that's displayed in place of any blank display characters. Each display character is a place holder in the mask where the user enters the characters as required by the mask. The default prompt character is underscore (_).
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2