This article describes the formula syntax of the XLL.ALERT.LEVEL function.
Set the current alert level using a mask and return the old mask.
XLL.ALERT.LEVEL(level)
level is the alert level mask to set.
The xll library can report errors, warnings, and information using pop-up alerts.
These can be turned on or off using any sum of XLL_ALERT_ERROR(),
XLL_ALERT_WARNING(), or XLL_ALERT_INFO() flags.
The function returns the previous mask and the argument
is stored at HKEY_CURRENT_USER\Software\KALX\xll\xll_alert_level
in the registry to persist across Excel sessions.