It seems their main point is using HTML is trading accessibility and security concerns for prettification. Why is a reference document an acceptable trade off of accessibility and security concerns for prettier formatting but a personal email isn't?
They could have made this site plain text and followed all of their own guidelines, but they didn't. Instead, they wanted to make the site look prettier to get their message across with additional formatting plain text can't handle. They're reducing accessibility and increasing security issues just for their own superfluous desires.
They could have made this site plain text and followed all of their own guidelines, but they didn't. Instead, they wanted to make the site look prettier to get their message across with additional formatting plain text can't handle. They're reducing accessibility and increasing security issues just for their own superfluous desires.