I can't seem to find any documentation on the Flex 4 ComboBox's prompt? in Flex 3 there was a simple prompt property available at the -1 index - however I can't seem to find anything similiar in the Flex 4 / Spark Combobox?
Unfortunately the prompt functionality did not make it into Flex 4 for the Spark ComboBox. Look for ComboBox and TextInput prompt support in a future release.
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