Empty and nested optgroup elements

Item one Item inside an optgroup without a labelItem inside an optgroup with an empty label Item twoItem three Item four

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

The text of the rows of the dropdown must not overlap each other.