About opening of links in new tabs or browser windows (Features)
your code is invalid and that's the point. Of course, browsers may have a "tolerance" level and will "support" the deprecated attribute. Changing from strict to transitional solves this problem, the resulting code is valid.
It's like car driving: If there is a 30km/h limit, you can also drive 50km/h. Your car will "support" this "feature". The question ist: Why don't you use the highway to drive faster - in a legal manner?
My code is invalid only according to canonical/arbitrary rule and that's the point.
Browsers are supporting a de facto standard not out of "tolerance" but out of principle which is called common law.
According to the common law principle which browsers adopted rightfully - my code is 100% legal and 100% valid.