HTML5 and target=_new usage. Yes, this use will fail in browsers that adhere to strict HTML rules. Just because a browser allows us to use some intuitive code doesn't mean that the usage should be correct. It is like a spellcheck. Professional or well studied html coders never use the target="_new" instruction with the underscore ( _ ) in their code and thus never have a problem with it. It demonstrates bad form.
So how do we use target=_new in HTML 5?
Datum: This html 5 usage is correct: <a href="your link goes here" target="new" >
Datum: This html 5 usage is not correct: <a href="your link goes here" target="_new">.
Background information: There are four reserved HTML uses that can start with <a target="_... and target="_new" is not one of them. This type of attempted usage would fall under a category like "all other random uses" which is governed by a naming etiquette and target="_new" fails the usage test.