Why does CSS work with fake elements?

Question

In my class, I was playing around and found out that CSS works with made-up elements.

Example:

Answer 1

Surprisingly, nobody (including my past self) mentioned accessibility. Another reason that using valid tags instead of custom ones is for compatibility with the greatest amount of software, including screen-readers and other tools that people need for accessibility purposes. Moreover, accessibility laws like WAI require making accessible websites, which generally means requiring them to use valid markup.

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^{Apparently nobody mentioned it, so I will.}

This is a by-product of browser wars.

Back in the 1990’s when the Internet was first starting to go mainstream, competition incrased in the browser market. To stay competitive and draw users, some browsers (most notably Internet Explorer) tried to be helpful and “user-friendly” by attempting to figure out what page designers meant and thus allowed markup that are incorrect (e.g., foobar would correctly render as bold-italics).

This made sense to some degree because if one browser kept complaining about syntax errors while another ate anything you threw at it and spit out a (more-or-less) correct result, then people would naturally flock to the latter.

While many thought the browser wars were over, a new war between browser vendors has reignited in the past few years since Chrome was released, Apple started growing again and pushing Safari, and IE lost its dominance. (You could call it a “cold war” due to the perceived cooperation and support of standards by browser vendors.) Therefore, it is not a surprise that even contemporary browsers which supposedly conform strictly to web standards actually try to be “clever” and allow standard-breaking behavior such as this in order to try to gain an advantage as before.

Unfortunately, this permissive behavior led to a massive (some might even say cancerous) growth of poorly marked up webpages. Because IE was the most lenient and popular browser, and due to Microsoft’s continued flouting of standards, IE became infamous for encouraging and promoting bad design and propagating and perpetuating broken pages.

You may be able to get away with using quirks and exploits like that on some browsers for now, but other than the occasional puzzle or game or something, you should always stick to web standards when creating web pages and sites to ensure they display correctly and avoid them becoming broken (possibly completely ignored) with a browser update.