People have adapted their habits and attitudes to the design of the Web and the Internet in general…up to a point. The world of the Web is a lot bigger than the subjective worlds in which most of its users live—it’s worldwide, in fact!—which makes for some interesting quirks in the system.
Given brokered advertising, blog comments, social media snippets, and the avalanche of third-party content that may well end up on your website, you can’t realistically hope that documents will remain as pristine as they were when you put them into production.
Put more bluntly, not everybody has your chops.
Unfortunately, this is a challenge that cannot be avoided or solved, even though it can be attenuated by relying on Transitional document types. Sometimes garbage will find its way onto your sites. Live with it.
Educate as many visitors and third-party content providers as you can without damaging your workflow and lifestyle, and in the meantime use the sturdiest markdown tools you can find to process things like user comments.
This is among the worst of the Bad Parts—not because it exemplifies a practice to be avoided, but because it illuminates one of the most intractable flaws of the HTML+CSS system.
Put simply, when you fail to insert a closing tag or foul
class value, you also inadvertently cause the
working cascade to deviate from the one that you’ve designed. ...