Board Thread:Wikia Discussion/@comment-25683568-20150318062713/@comment-26154973-20150731090546

The only usage for ' or - I know is for ん before vowels and y (https://en.wikipedia.org/wiki/Hepburn_romanization#Syllabic_n), so Junyou should be じゅにょう, while じゅんよう is Jun'you.

Though you can see example such as


 * 金曜日（きんようび）: ki + n + yo + u + bi = kinyōbi[14] or kin'yōbi[15] – Friday

in the same article, so maybe we can consider it optional and don't use it.