A custom listHTML has been provided here, so that the display doesn't have to match the value of the selection.
Also, this has autoShow set to false, which is why the drop-down doesn't automatically appear when you click on the text field.
The combobox picks up the "value" attribute from each option, and uses that as the value of the selection. This lets you use different values for the display vs. the actual value.
This is alt text, where the combobox would be
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This demonstrates how to pull values out of an external dictionary, mapping tech companies to their websites. It also shows how to include images in the list.