This property is not used by any of the predefined dialogs used by the WebHtmlEditor. However, you may set this property if you would like to supply the content for the dialog from a file on the server. If this is the case, the dialog will launch in a modal dialog box that you will not be able to modify the titlebar properties (such as TitlebarBackColor) of.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, 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