From Xojo Documentation

Property (As String )
aListBox.InitialValue = newStringValue
StringValue = aListBox.InitialValue

Supported for all project types and targets.

A list of the default items separated by returns.


If the ListBox has more than one column (ColumnCount > 1), separate column entries with Tabs within each row. If HasHeading is True, the first row of InitialValue is assumed to be the column headings -- unless the Heading array is also specified.