I'm slightly confused by the combination of "introduced in Internet Explorer 5.5" and "offers a powerful new way" being written in an article posted on August 28, 2017
FTA: cough OK, obviously it’s 2017 and Internet Explorer 5.5 isn’t relevant anymore. But if you’re a Web developer, this should have given you some pause for thought. The modern Web Components pillars: Templates, Custom Elements, Shadow DOM, and Imports, were all features originally in IE5, released in 1999.
haha, it really was too, no hint of sarcasm! Young'uns these days probably can't believe what a saviour Microsoft from the clusterfudge that Navigator represented back then.