Abbreviations are the heart of the Emmet toolkit: these special expressions are parsed in runtime and transformed into structured code block, HTML for example. The abbreviation’s syntax looks like CSS selectors with a few extensions specific to code generation. So every web-developer already knows how to use it.
Here’s an example: this abbreviation
#page>div.logo+ul#navigation>li*5>a{Item $}
...can be transformed into
<div id="page">
<div class="logo"></div>
<ul id="navigation">
<li><a href="">Item 1</a></li>
<li><a href="">Item 2</a></li>
<li><a href="">Item 3</a></li>
<li><a href="">Item 4</a></li>
<li><a href="">Item 5</a></li>
</ul>
</div>