> ASCII is a character set, it doesn't define the on-disk representation. ASCII is both a character set and an encoding. The encoding specifies 8 bits per char

> ASCII is a character set, it doesn't define the on-disk representation. ASCII is both a character set and an encoding. The encoding specifies 8 bits per character with the high bit clear. Every file encoded this way is also valid UTF-8. That's what the article's statement meant.