1..7
# ->configure()
 -  throws an InvalidArgumentException if a currency does not exist
 -  can restrict the number of currencies with the currencies option
# ->render()
 -  renders all currencies as option tags
 -  renders all currencies as option tags
 -  does not output ICU dummy data
# add_empty
 -  renders an empty option if add_empty is true
 -  renders an empty option if add_empty is true
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