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<h1 class="entry-title">Using the Attribute Selector with Numeric Values</h1>
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<time datetime="2012-09-19T20:42:00-04:00" pubdate data-updated="true">Sep 19<span>th</span>, 2012</time>
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<div class="entry-content"><p>What color will the number 3 be in the example below?</p>
<figure class='code'><figcaption class='empty'><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
<span class='line-number'>13</span>
<span class='line-number'>14</span>
</pre></td><td class='code'><pre><code class='html'><span class='line'><span class="nt"><style></span>
</span><span class='line'> <span class="nt">td</span> <span class="p">{</span> <span class="k">color</span><span class="o">:</span> <span class="nb">red</span><span class="p">;</span> <span class="p">}</span>
</span><span class='line'> <span class="nt">td</span><span class="o">[</span><span class="nt">colspan</span><span class="o">=</span><span class="nt">2</span><span class="o">]</span> <span class="p">{</span> <span class="k">color</span><span class="o">:</span> <span class="nb">blue</span><span class="p">;</span> <span class="p">}</span>
</span><span class='line'><span class="nt"></style></span>
</span><span class='line'>
</span><span class='line'><span class="nt"><table></span>
</span><span class='line'> <span class="nt"><tr></span>
</span><span class='line'> <span class="nt"><td</span> <span class="na">colspan=</span><span class="s">"2"</span><span class="nt">></span>1<span class="nt"></td></span>
</span><span class='line'> <span class="nt"></tr></span>
</span><span class='line'> <span class="nt"><td></span>
</span><span class='line'> <span class="nt"><td></span>2<span class="nt"></td></span>
</span><span class='line'> <span class="nt"><td></span>3<span class="nt"></td></span>
</span><span class='line'> <span class="nt"></tr></span>
</span><span class='line'><span class="nt"></table></span>
</span></code></pre></td></tr></table></div></figure>
<p>Turns out it will be red because the <code>td[colspan=2]</code> selector does not match it. Why?</p>
<!--more-->
<h3>Attribute Selector</h3>
<p>Per the <a href="http://www.w3.org/TR/css3-selectors/#attribute-selectors">CSS 3 specification</a> values used in attribute selectors must be either identifiers or strings.</p>
<p>String values are those enclosed by single or double quotes (e.g. the <code>2</code> in the selector <code>value="2"</code>). If a value is not a string the browser attempts to resolve it as an identifier, which the spec defines as such:</p>
<blockquote><p>“In CSS, identifiers (including element names, classes, and IDs in selectors) can contain only the characters [a-zA-Z0-9] and ISO 10646 characters U+00A0 and higher, plus the hyphen (-) and the underscore (_); they cannot start with a digit, two hyphens, or a hyphen followed by a digit.”</p><footer><strong>CSS 2.1 Specification</strong> <cite><a href='http://www.w3.org/TR/CSS2/syndata.html#value-def-identifier'>www.w3.org/TR/CSS2/…</a></cite></footer></blockquote>
<p>So why doesn’t <code>colspan=2</code> work above? The key part from the spec is that ”<em>identifiers … cannot start with a digit</em>”. Therefore, since <code>2</code> is not a string and does not qualify as an identifier, the browser ignores it. This behavior is implemented consistently in all browsers.</p>
<p>The fix? Simply wrap the value in quotes; both <code>td[colspan='2']</code> and <code>td[colspan="2"]</code> will match the cell in the example above.</p>
<h3>Numeric Attributes</h3>
<p>Attributes that generally only have numeric values include <code>colspan</code>, <code>rowspan</code>, <code>cellpadding</code>, <code>cellspacing</code>, <code>min</code>, <code>max</code>, and <code>step</code>. When using any of these attributes in an attribute selector ensure that you wrap the value in quotes.</p>
<h3>JavaScript</h3>
<p>Most selector engines such as jQuery’s sizzle will make the selector work regardless of whether the quotes are present. <code>$('td[colspan=2]')</code> will return the cell in question in the example above.</p>
<p>However, if you are using native JavaScript though you will not be so lucky; <code>document.querySelectorAll('td[colspan=2]')</code> actually throws an error.</p>
<h3>Conclusion</h3>
<p>Attributes with numeric values need to have quotes around them when using them in CSS or JavaScript. When in doubt use quotes around attribute values; it never hurts, and there are some strange edge cases where omitting the quotes leads to unexpected behavior. If you’re looking for a more detailed writeup on when quotes are ok to omit checkout <a href="http://mathiasbynens.be/notes/unquoted-attribute-values">Mathias Bynens’ writeup on the topic</a>.</p>
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<time datetime="2012-09-19T20:42:00-04:00" pubdate data-updated="true">Sep 19<span>th</span>, 2012</time>
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