> HTML has always ignored them. No, browsers have always ignored them. Until HTML5 came along, they were the start of a NET. It was incorrect syntax that woul

> HTML has always ignored them. No, browsers have always ignored them. Until HTML5 came along, they were the start of a NET. It was incorrect syntax that would probably end up causing a parse error later in the document thus mangling it. However because browsers didn't fully comply with SGML-based HTML parsing, the mangling didn’t happen and the result was that this syntax mistake would have no effect. Two bugs cancelling each other out. That is a different situation to HTML5, which explicitly states that it’s an acceptable no-op. “This is okay, but you don’t need to do anything with it” is a different situation to “This is a NET” followed by “I don’t know what a NET is, so I’m going to mis-parse it as an attribute and then ignore it because it makes no sense as an attribute”.