`idna` accepts Punycode labels that do not produce any non-ASCII when decoded
idna 0.5.0 and earlier accepts Punycode labels that do not produce any non-ASCII output, which means that either ASCII labels or the empty root label can be masked such that they appear unequal without IDNA processing or when processed with a different implementation and equal when processed with idna 0.5.0 or earlier. Concretely, example.org and xn–example-.org become equal after processing by idna 0.5.0 or earlier. Also, example.org.xn– and example.org. become …