The drop down box's values are populated from an class called
a data provider, which returns a list of values based on the characters
that the user has typed into the input box.
If OPTION tags are used as the data provider via markup,
then the OPTION tag's child text node is used as the widget value
when selected. The OPTION tag's value attribute is ignored.
To set the default value when using OPTION tags, specify the selected
attribute on 1 of the child OPTION tags.
Some of the options to the ComboBox are actually arguments to the data
provider.