SEO-friendly URLs and relative links

The Web community is going crazy about SEO-friendly URLs like http://somesite.com/products/network/router/. Well, it looks much better than a script URL http://somesite.com/products.php?c=network&p=router which may actually serve the page behind the scenes. There are a lot of good articles on how to implement SEO-friendly URLs, for example this one or my own post. But they do not warn the reader about one usual problem: once you have updated your site to handle virtual paths you will probably get a bad surprise:

CSS, image and internal page links are totally broken!

Why? Because those links are usually relative to the page location. The browser has no idea about virtual folders and tries to get files from locations relative to the page URL context. For example, if there is a usual CSS link in the page header:

<link rel="stylesheet" href="style.css" type="text/css" media="screen" />

Then the browser will try to download non-existing file http://somesite.com/products/network/router/style.css and fail silently. No CSS style will be applied.

It’s incredible how many words were spoken about SEO-friendly URLs with almost no word about this relative link problem.
So, what you have to do? Don’t worry, there are multiple solutions available and I’ll try to explain them all.

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