This is a Response Button Handling style constant used by the SalMessageBox function to specify that the first button (usually Ok) has the focus when the dialog box displays. You can combine a Response Button Handling style constant with a constant from the Icon style, System Options style, and Push Button style constant groups (all of which are also named MB_*) using the OR (|) operator. See SalMessageBox Options and SalMessageBox Returns for more information. Value = 0

public const int MB_DefButton1