Shorthand syntax has the potential to introduce **breakage**

[thierryk]

Let's imagine this scenario:

HTML

<div class="module news">
   ...
</div>

CSS

.module {
    background-color: #fff;
}
.news {
    background-image: url('smiley.gif');
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-position: center;
}

If shrthnd.js converts the above into this:

.module {
    background-color: #fff;
}
.news {
  background: url('smiley.gif') no-repeat fixed center;
}

Then .news.module will end up with a transparent background color (instead of white) because the shorthand rule "resets" the value of background-color to its initial value—which is transparent.