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In the XUI-Editor go to the appropriate node and create a XUI Component if necessary. Select "Style" > "Choice" and set the "Visualizer type" to advancedComboBox. The component itself will be configured with a HTML escaped JSON String in the forms NLS file. For Example:
/rootNode/choice/fahrt%label%choice={"label"&co;"Lokale Verteilfahrt", "desc"&co;"Beschreibung", "imgClass"&co;"lokaleVerteilfahrt"}
This NLS Entry for one element will be rendered as follow:
For layouting the widget there are several CSS Classes applied to the component to format it to your needs.