Siemens SIMATIC HMI Series System Manual page 180

WinCC diagnosis
6.3 ApDiag Menu Commands
Note
"MB_SYSTEMMODAL" parameter
Execution of a message box function with parameter "MB_SYSTEMMODAL" ensures that the
message box is displayed in the foreground. If this parameter is not specified, the message
box is hidden to users and (in the background) and cannot be operated. Mouse click events
outside the message box are written to a buffer and processed after you exit the message box.
Example: MessageBox(NULL, "Welt", "Hallo", MB_SYSTEMMODAL | MB_OK);
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WinCC: General information and installation
System Manual, 02/2017, A5E40840020-AA