ComboBox.Hint
From Xojo Documentation
Property (As String )
aComboBox.Hint = newStringValue
or
StringValue = aComboBox.Hint
New in 2019r2
Supported for all project types and targets.
or
StringValue = aComboBox.Hint
New in 2019r2
Supported for all project types and targets.
Text that appears in the Combobox when the ComboBox.Value property is empty.
Notes
Use ComboBox.Hint to provide additional context regarding the type of information the user should be entering or choosing from the menu.
Sample Code
This code assigns text to the ComboBox.Hint property of a ComboBox named "School".
School.Hint = "Choose a School"