Click on the select element above. When it drops down you should see the following items in the list:

• Item one
• Group one
• Group two
• (unselectable, empty row)
• Item inside an optgroup without a label
• (unselectable, empty row)
• Item inside an optgroup with an empty label
• (selectable, empty row)
• Group three
• Item two
• Nested group 1
• Nested group 2
• Nested group 3
• Item three
• Item four