Behold - the shiny "feature" of html5 - "import" for including web "packages" with a simple link. This is the equivalnce of "include" in many other languages with one powerful rule - you can include a resource which can import several assets - css, js and html templates.
Take "bootstrap" for example. Bootstrap includes few files that should be loaded: css files, js file and perhaps other (for custom themes etc..).
With "import" feature, it can be done easily with a simple line:
<link rel="import" href="bootstrap.html">
checkout the full article at html5rocks for more info.