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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no" />
<meta http-equiv="X-UA-Compatible" content="IE=Edge" />
<title>length-property: length \0; hack – CSS Hacks Lab</title>
<link href="../../microstrap.css" rel="stylesheet" />
<style>
.testbed {
height: 100px;
width: 100px;
line-height: 100px;/* vertical centering trick */
white-space: nowrap;
font-family: Helvetica,Arial,sans-serif;
font-weight: bold;
font-size: large;
position: relative;/* to make abspos child work properly; blame CSS logic */
}
.testbed-margin {
overflow: hidden;
}
.liquid {
height: 100%;
width: 100%;
}
.guineapig {
position: absolute;
top: 0;
left: 0;
}
.guineapig-padding {
width: 0;
height: 0;
}
.guineapig-wh {
width: 0px;
height: 0px;
overflow: hidden;
}
.guineapig-margin {
position: absolute;
left: 100px;
}
.guineapig-border-width {
width: 0;
height: 0;
border-style: solid;
border-color: limegreen;
border-width: 0;
}
</style>
<!-- Operative part of the test: -->
<style>
.guineapig-padding {
padding-right: 100px \0;
padding-bottom: 100px \0;
}
</style>
<style>
.guineapig-wh {
width: 100px \0;
height: 100px \0;
}
</style>
<style>
.guineapig-margin {
margin-left: -100px \0;
}
</style>
<style>
.guineapig-border-width {
border-right-width: 100px \0;
border-bottom-width: 100px \0;
}
</style>
</head>
<body>
<div class="container">
<h1>The <code>length-property: length \0;</code> hack</h1>
<p>Last updated 2016-02-02.</p>
<h2>The hack</h2>
<div class="scroll-x">
<pre>
.your-selector-here {
some-length-property-here: somelength \0;
}
</pre>
</div>
<p>…where <code>somelength</code> is a <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/length">CSS length value</a> and <code>some-length-property-here</code> is a CSS property whose value can be a CSS length.</p>
<!--
FIXME: WHAT ABOUT PERCENT LENGTHS?
-->
<p>
Source: <a href="http://www.paulirish.com/2009/browser-specific-css-hacks/">Browser CSS Hacks</a> by Paul Irish
</p>
<p>
<strong>Important note!</strong>
This article <strong>only</strong> applies to the specific properties mentioned below and <strong>only</strong> applies when there is space between <code>somelength</code> and <code>\0</code>.
Adding spaces or using different properties <em>changes the compatibility of the hack</em>.<br />
You have been warned.
</p>
<h2 id="tests">Live testcases</h2>
<div class="testbed text-center">
<div class="yes guineapig guineapig-wh">Affected</div>
<div class="no">Unaffected</div>
</div>
<p>If the square above shows the word "Affected", then your browser supports this hack for the <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/width"><code>width</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/height"><code>height</code></a> CSS properties.</p>
<div class="testbed testbed-margin text-center">
<div class="guineapig-margin liquid yes">Affected</div>
<div class="liquid no">Unaffected</div>
</div>
<p>If the square above shows the word "Affected", then your browser supports this hack for the <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/margin"><code>margin-{top,bottom,left,right}</code></a> CSS properties.</p>
<div class="testbed no">
<div class="guineapig-padding yes"></div>
</div>
<p>If the above square is light green, then your browser supports this hack for the <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/padding"><code>padding-{top,bottom,left,right}</code></a> CSS properties.</p>
<div class="testbed no">
<div class="guineapig-border-width"></div>
</div>
<p>If the above square is light green, then your browser supports this hack for the <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/margin"><code>border-{top,bottom,left,right}-width</code></a> CSS properties.</p>
<h2 id="how-it-works">How it works</h2>
<p>
<a href="https://drafts.csswg.org/css-syntax/#escaping">Backslash (<code>\</code>) is used as an escape character in CSS.</a> So <code>\0</code> is an escape sequence which notionally encodes the <a href="https://en.wikipedia.org/wiki/Null_character">null character (␀).</a>
However, presumably to prevent bugs related to potential use of <a href="https://en.wikipedia.org/wiki/Null-terminated_string">null-terminated strings</a> in browser implementations, the <a href="https://drafts.csswg.org/css-syntax/#consume-escaped-code-point">CSS Syntax Module Level 3 specifically treats <code>\0</code> like an invalid escape sequence</a> and requires that it result in the <a href="https://en.wikipedia.org/wiki/Specials_%28Unicode_block%29#Replacement_character">Unicode replacement character (U+FFFD; "�")</a> instead of the null character.
But CSS Syntax Level 3 is a somewhat recent spec, and thus older browsers treat <code>\0</code> differently.
</p>
<p>At any rate, there are 4 obvious ways that browsers might parse <code><em>somelength</em> \0</code>:</p>
<ol>
<li>As <code><em>somelength</em> �</code>, per the CSS Syntax Level 3 spec.</li>
<li>As <code><em>somelength</em> ␀</code>, assuming the browser doesn't use null-terminated strings internally and doesn't treat null characters in CSS as syntax errors.</li>
<li>As <code><em>somelength</em> </code>, assuming the browser does use null-terminated strings internally and doesn't treat null characters in CSS as syntax errors. To be clear, this is a blatant implementation bug in the browser.</li>
<li>As a syntax error. Prior to CSS Syntax Level 3, this was a reasonable choice for savvy parsers, since it's difficult to come up with any legitimate use for null characters in CSS.</li>
</ol>
<p>
Cases 1 & 2 will ultimately lead to syntax errors, since neither <code> �</code> nor <code> ␀</code> can be part of valid <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/length">CSS length values</a>.
</p>
<p>That leaves Case 3, which will lead to the ␀ itself and any content after it being ignored since the ␀ will terminate the string prematurely, leaving (in the case of this hack) only a valid length (and some permissible trailing whitespace) as the property's value.</p>
<p>This hack is known to be compatible with IE8-10. It is known to <em>not</em> be compatible with IE11, in contrast to <a href="../../property-value-backslash-0/length/">the spaceless counterpart</a> of this hack.</p>
<h2 id="compat">Affected browsers</h2>
<p>Check out the links for corroborating screenshots.</p>
<div class="scroll-x">
<table class="table table-bordered">
<caption>Test results</caption>
<thead class="thead-browsers">
<tr>
<th>
<img src="../../browser-imgs/chrome_64x64.png" alt="Chrome" /><br />
</th>
<th>
<img src="../../browser-imgs/safari-osx_64x64.png" alt="OS X Safari" /><br />
</th>
<th>
<img src="../../browser-imgs/safari-ios_64x64.png" alt="iOS Safari" /><br />
</th>
<th>
<img src="../../browser-imgs/firefox_64x64.png" alt="Firefox" /><br />
</th>
<th>
<img src="../../browser-imgs/edge_64x64.png" alt="Microsoft Edge" /><br />
</th>
<th>
<img src="../../browser-imgs/ie_64x64.png" alt="Internet Explorer" /><br />
</th>
</tr>
<tr>
<th>Chrome</th>
<th>OS X<br />Safari</th>
<th>iOS<br />Safari</th>
<th>Firefox</th>
<th>MS Edge<a href="#edgenote"><sup>1</sup></a></th>
<th>Internet<br />Explorer</th>
</tr>
</thead>
<tbody>
<tr>
<td class="unknown">
49
<br />Unknown
</td>
<td class="unknown">
10
<br />Unknown
</td>
<td class="unknown">
9.3
<br />Unknown
</td>
<td class="unknown">
45
<br />Unknown
</td>
<td class="unknown">
13
<br />Unknown
</td>
<td class="empty"></td>
</tr>
<tr>
<td class="no">
48
<br /><a href="chrome/v48.png">Unaffected</a>
</td>
<td class="no">
9.0.3
<br /><a href="safari-osx/v9-0-3.png">Unaffected</a>
</td>
<td class="no">
9.2
<br /><a href="safari-ios/v9-2.png">Unaffected</a>
</td>
<td class="no">
44.0
<br /><a href="firefox/v44-0.png">Unaffected</a>
</td>
<td class="no">
12.10240
<br /><a href="edge/v12-10240.png">Unaffected</a>
</td>
<td class="no">
11
<br /><a href="ie/v11.png">Unaffected</a>
</td>
</tr>
<tr>
<td class="no">
47
<br /><a href="chrome/v47.png">Unaffected</a>
</td>
<td class="no">
8.0.8
<br /><a href="safari-osx/v8-0-8.png">Unaffected</a>
</td>
<td class="no">
8.4
<br /><a href="safari-ios/v8-4.png">Unaffected</a>
</td>
<td class="no">
43.0.1
<br /><a href="firefox/v43-0-1.png">Unaffected</a>
</td>
<td class="unknown">
12.10166
<br />Unknown
</td>
<td class="yes">
10
<br /><a href="ie/v10.png">Affected</a>
</td>
</tr>
<tr>
<td class="no">
26
<br /><a href="chrome/v26.png">Unaffected</a>
</td>
<td class="no">
7.1.7
<br /><a href="safari-osx/v7-1-7.png">Unaffected</a>
</td>
<td class="no">
7.1
<br /><a href="safari-ios/v7-1.png">Unaffected</a>
</td>
<td class="no">
4.0.1
<br /><a href="firefox/v4-0-1.png">Unaffected</a>
</td>
<td class="empty"></td>
<td class="yes">
9
<br /><a href="ie/v9.png">Affected</a>
</td>
</tr>
<tr>
<td class="unknown">
25
<br />Unknown
</td>
<td class="unknown">
6.2.7
<br />Unknown
</td>
<td class="unknown">
6.1
<br />Unknown
</td>
<td class="empty"></td>
<td class="empty"></td>
<td class="yes">
8
<br /><a href="ie/v8.png">Affected</a>
</td>
</tr>
<tr>
<td class="empty"></td>
<td class="empty"></td>
<td class="empty"></td>
<td class="empty"></td>
<td class="empty"></td>
<td class="unknown">
7
<br />Unknown
</td>
</tr>
</tbody>
</table>
</div>
<small class="note" id="edgenote">Note 1: MS Edge versions refer to the EdgeHTML rendering engine version, not the Edge app version shown in Edge's "About" screen. <a href="https://github.com/Fyrd/caniuse/issues/1928">See this <em>Can I Use</em> issue.</a></small><br />
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