When I have written "音読み{おんよみ}" and "訓読み{くんよみ}" in romaji as: "onyomi" and "kunyomi" I have been almost always corrected. "Onyomi" is changed to "on'yomi", and "kunyomi" is changed to "kun'yomi".
(1) Are these corrections made because "音読み" and "訓読み" are 重箱読み{じゅうばこよみ}?
(2) Is inserting a single quote between the "on" and "kun" readings in a "重箱読み" a standard convention (and not just the editor's preference)? A url link to information regarding this convention would be appreciated. I'm interested in any/all conventions for writing in romaji.
(3) If I am indeed being corrected because they are 重箱読み、 then by extension all 重箱読み, when written in romaji, should have a single quote between the "on" and "kun" readings, right?