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    <blockquote> <p>Which is faster?</p> </blockquote> <p>Like Cody and thirtydot said, theoretically using <code>&gt;</code> should be faster, but even styling for IE6 is less a waste of your time than styling for performance. Browsers are <em>fast enough</em>; trust your <em>browsers</em>, not the <em>people</em> who tell you this, especially not those who don't provide any <em>browser</em> benchmarks to back their claims.</p> <blockquote> <p>any reliability problem for any of this?</p> </blockquote> <p>Sure. Besides IE6 not supporting <code>&gt;</code> at all as thirtydot mentions, there's also the difference in elements matched since <code>&gt;</code> and the whitespace combinators select different things:</p> <pre><code>&lt;section class="slide"&gt; &lt;div&gt; &lt;span&gt;&lt;/span&gt; &lt;!-- [1] --&gt; &lt;div&gt; &lt;span&gt;&lt;/span&gt; &lt;!-- [2] --&gt; &lt;/div&gt; &lt;/div&gt; &lt;div&gt; &lt;p&gt; &lt;span&gt;&lt;/span&gt; &lt;!-- [3] --&gt; &lt;/p&gt; &lt;/div&gt; &lt;/section&gt; </code></pre> <p>What's selected and what's not:</p> <ol> <li><p><strong>Selected by both selectors</strong><br> This <code>span</code> is a child of a <code>div</code> which is a child of an element with class <code>slide</code>. Since <code>span</code> is a child of <code>div</code>, it's also a descendant of <code>div</code>. Likewise for <code>div</code> and its <code>.slide</code> parent/ancestor.</p> <p>On hovering the <code>.slide</code> element, this <code>span</code> is selected. The rule applied is the second one because both selectors are of equal specificity, but the second one, well, comes second.</p></li> <li><p><strong>Selected only by <code>.slide:hover div span</code></strong><br> This <code>span</code> is in a <code>div</code>, <em>but</em> its parent <code>div</code> is located in <em>another</em> <code>div</code> that doesn't have the class <code>slide</code>. So the first selector doesn't find this element.</p> <p>The inner parent <code>div</code> is, however, a grandchild of a <code>.slide</code> element. Regardless of depth, it's still in some way a descendant of <code>.slide</code> (it's contained somewhere within it).</p> <p>On hovering the <code>.slide</code> element, this <code>span</code> is selected. The rule applied is the second one because it's the only one that matches.</p></li> <li><p><strong>Selected only by <code>.slide:hover div span</code></strong><br> This <code>span</code>'s parent is a <code>p</code> element, not a <code>div</code>. Easy enough; the first selector doesn't find this element.</p> <p>The <code>span</code> is, however, a grandchild of a <code>div</code> element, which itself is inside a <code>.slide</code>.</p> <p>On hovering the <code>.slide</code> element, this <code>span</code> is selected. The rule applied is the second one because it's the only one that matches.</p></li> </ol> <p>One last thing: in all three scenarios do you find that the rules in only the second selector are applied. <strong>This is purely coincidental</strong>; the differences in how supporting browsers look for elements to match are still real.</p>
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    1. POCSS: Does it render "ul > li" faster than "ul li"?
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    1. COSee. You know *way* more about CSS than I do. I'm a .NET/C++ developer that's just pretending. I still think my argument to thirtydot's post that using `<` and an extra space will "bloat" the code with more characters, also increasing loading time, is pretty good. Google worries about this sort of thing, so why shouldn't everyone? :-p
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      1. USCody Gray
    2. CO@Cody Gray: Well thanks. I just wasn't sure if it was worth the details for such a simple question - whether I was answering the right one anyway. I still believe you hit the nail right on the head, and deserve all 5 votes... after all, like Sayem said, KISS!
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    3. COThe thing is... the browser CSS engine developers are the ones who tell you to use `>` instead of space. But yes, for most uses it doesn't matter. It starts to matter once you have lots of rules, lots of elements, or lots of dynamic changes (or any combination of those). For example, loading the HTML5 single-page spec the selector matching is something like 25% of the load time, and a lot of that is due to its use of space in selectors.
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