Isn't it just two nested ternary operators? The equivalent being:
selected_value =
condition_1 ?
value_1 :
condition_2 ? value_2 : value_3 selected_value =
condition_1 ?
value_1 :
condition_2 ? value_2 : value_3 selected_value =
condition_1 ? value_1 :
condition_2 ? value_2 :
value_3