The leniency of HTML burned me a lot in my beginner days. At some point, I decided to switch to XHTML (serving as the media type "application/xhtml+xml") and ne

The leniency of HTML burned me a lot in my beginner days. At some point, I decided to switch to XHTML (serving as the media type "application/xhtml+xml") and never looked back. Ditto JavaScript, the laxness harmed a lot, and only like 15 years later did I prepend "use strict" to every script.