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[1.4.x?] Completed enduser-utf8.html
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Edward Z. Yang
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3
NEWS
3
NEWS
@ -9,6 +9,9 @@ NEWS ( CHANGELOG and HISTORY ) HTMLPurifier
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. Internal change
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==========================
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1.4.2, unknown release date
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! docs/enduser-utf8.html explains how to use UTF-8 and HTML Purifier
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1.4.1, released 2007-01-21
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! docs/enduser-youtube.html updated according to new functionality
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- YouTube IDs can have underscores and dashes
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@ -32,8 +32,14 @@ the fact that it operates UTF-8 or the limitations of the character
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encoding transformations it does. This document will walk you through
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determining the encoding of your system and how you should handle
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this information. It will stay away from excessive discussion on
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the internals of character encoding, but offer the information in
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asides that can easily be skipped.</p>
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the internals of character encoding.</p>
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<p>This document is not designed to be read from top to bottom: it will
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slowly introduce concepts that build on each other: you need not get to
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the bottom to have learned something new. However, I strongly
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recommend you read all the way to <strong>Why UTF-8?</strong>, because at least
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at that point you'd have made a conscious decision not to migrate,
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which can be a difficult but rewarding task.</p>
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<blockquote class="aside">
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<div class="label">Asides</div>
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@ -43,6 +49,50 @@ asides that can easily be skipped.</p>
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with a greater understanding of the underlying issues.</p>
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</blockquote>
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<h2>Table of Contents</h2>
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<ol id="toc">
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<li><a href="#findcharset">Finding the real encoding</a></li>
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<li><a href="#findmetacharset">Finding the embedded encoding</a></li>
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<li><a href="#fixcharset">Fixing the encoding</a><ol>
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<li><a href="#fixcharset-none">No embedded encoding</a></li>
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<li><a href="#fixcharset-diff">Embedded encoding disagrees</a></li>
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<li><a href="#fixcharset-server">Changing the server encoding</a><ol>
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<li><a href="#fixcharset-server-php">PHP header() function</a></li>
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<li><a href="#fixcharset-server-phpini">PHP ini directive</a></li>
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<li><a href="#fixcharset-server-nophp">Non-PHP</a></li>
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<li><a href="#fixcharset-server-htaccess">.htaccess</a></li>
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<li><a href="#fixcharset-server-ext">File extensions</a></li>
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</ol></li>
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<li><a href="#fixcharset-xml">XML</a></li>
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<li><a href="#fixcharset-internals">Inside the process</a></li>
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</ol></li>
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<li><a href="#whyutf8">Why UTF-8?</a><ol>
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<li><a href="#whyutf8-i18n">Internationalization</a></li>
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<li><a href="#whyutf8-user">User-friendly</a></li>
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<li><a href="#whyutf8-forms">Forms</a><ol>
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<li><a href="#whyutf8-forms-urlencoded">application/x-www-form-urlencoded</a></li>
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<li><a href="#whyutf8-forms-multipart">multipart/form-data</a></li>
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</ol></li>
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<li><a href="#whyutf8-support">Well supported</a></li>
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<li><a href="#whyutf8-htmlpurifier">HTML Purifiers</a></li>
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</ol></li>
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<li><a href="#migrate">Migrate to UTF-8</a><ol>
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<li><a href="#migrate-db">Configuring your database</a><ol>
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<li><a href="#migrate-db-legit">Legit method</a></li>
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<li><a href="#migrate-db-binary">Binary</a></li>
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</ol></li>
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<li><a href="#migrate-editor">Text editor</a></li>
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<li><a href="#migrate-bom">Byte Order Mark (headers already sent!)</a></li>
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<li><a href="#migrate-fonts">Fonts</a><ol>
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<li><a href="#migrate-fonts-obscure">Obscure scripts</a></li>
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<li><a href="#migrate-fonts-occasional">Occasional use</a></li>
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</ol></li>
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<li><a href="#migrate-variablewidth">Dealing with variable width in functions</a></li>
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</ol></li>
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<li><a href="#externallinks">Further Reading</a></li>
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</ol>
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<h2 id="findcharset">Finding the real encoding</h2>
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<p>In the beginning, there was ASCII, and things were simple. But they
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@ -401,7 +451,7 @@ ISO-8859-1 encoding (you see this in garbled RSS feeds).</p>
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trouble of adding the XML header, make sure it jives
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with your <code>META</code> tags and HTTP headers.</p>
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<h3>Inside the process</h3>
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<h3 id="fixcharset-internals">Inside the process</h3>
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<p>This section is not required reading,
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but may answer some of your questions on what's going on in all
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@ -781,7 +831,7 @@ To find out how your editor is doing, you can check out <a
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href="http://www.alanwood.net/unicode/utilities_editors.html">this list</a>
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or <a href="http://en.wikipedia.org/wiki/Comparison_of_text_editors#Encoding_support">Wikipedia's list.</a>
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I personally use Notepad++, which works like a charm when it comes to UTF-8.
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You will usually have to <strong>explicitly</strong> tell the editor through some dialogue
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Usually, you will have to <strong>explicitly</strong> tell the editor through some dialogue
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(usually Save as or Format) what encoding you want it to use. An editor
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will often offer "Unicode" as a method of saving, which is
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ambiguous. Make sure you know whether or not they really mean UTF-8
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@ -825,15 +875,153 @@ sure the page is saved WITHOUT the BOM.</p>
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</blockquote>
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<p>If you are reading in text files to insert into the middle of another
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page, it is strongly advised that you replace out the UTF-8 byte
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sequence for BOM <code>"\xEF\xBB\xBF"</code> before inserting it in.</p>
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page, it is strongly advised (but not strictly necessary) that you replace out the UTF-8 byte
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sequence for BOM <code>"\xEF\xBB\xBF"</code> before inserting it in,
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via:</p>
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<pre>$text = str_replace("\xEF\xBB\xBF", '', $text);</pre>
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<h3 id="migrate-fonts">Fonts</h3>
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<p>Generally speaking, people who are having trouble with fonts fall
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into two categories:</p>
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<ul>
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<li>Those who want to
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use an extremely obscure language for which there is very little
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support even among native speakers of the language, and</li>
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<li>Those where the primary language of the text is
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well-supported but there are occasional characters
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that aren't supported.</li>
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</ul>
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<p>Yes, there's always a chance where an English user happens across
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a Sinhalese website and doesn't have the right font. But an English user
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who happens not to have the right fonts probably has no business reading Sinhalese
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anyway. So we'll deal with the other two edge cases.</p>
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<h4 id="migrate-fonts-obscure">Obscure scripts</h4>
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<p>If you run a Bengali website, you may get comments from users who
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would like to read your website but get heaps of question marks or
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other meaningless characters. Fixing this problem requires the
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installation of a font or language pack which is often highly
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dependent on what the language is. <a href="http://bn.wikipedia.org/wiki/%E0%A6%89%E0%A6%87%E0%A6%95%E0%A6%BF%E0%A6%AA%E0%A7%87%E0%A6%A1%E0%A6%BF%E0%A6%AF%E0%A6%BC%E0%A6%BE:Bangla_script_display_help">Here is an example</a>
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of such a help file for the Bengali language, I am sure there are
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others out there too. You just have to point users to the appropriate
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help file.</p>
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<h4 id="migrate-fonts-occasional">Occasional use</h4>
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<p>A prime example of when you'll see some very obscure Unicode
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characters embedded in what otherwise would be very bland ASCII are
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letters of the
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<a href="http://en.wikipedia.org/wiki/International_Phonetic_Alphabet">International
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Phonetic Alphabet (IPA)</a>, use to designate pronounciations in a very standard
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manner (you probably see them all the time in your dictionary). Your
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average font probably won't have support for all of the IPA characters
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like ʘ (bilabial click) or ʒ (voiced postalveolar fricative).
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So what's a poor browser to do? Font mix! Smart browsers like Mozilla Firefox
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and Internet Explorer 7 will borrow glyphs from other fonts in order
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to make sure that all the characters display properly.</p>
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<p>But what happens when the browser isn't smart and happens to be the
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most widely used browser in the entire world? Microsoft IE 6
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is not smart enough to borrow from other fonts when a character isn't
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present, so more often than not you'll be slapped with a nice big �.
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To get things to work, MSIE 6 needs a little nudge. You could configure it
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to use a different font to render the text, but you can acheive the same
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effect by selectively changing the font for blocks of special characters
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to known good Unicode fonts.</p>
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<p>Fortunantely, the folks over at Wikipedia have already done all the
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heavy lifting for you. Get the CSS from the horses mouth here:
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<a href="http://en.wikipedia.org/wiki/MediaWiki:Common.css">Common.css</a>,
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and search for ".IPA" There are also a smattering of
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other classes you can use for other purposes, check out
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<a href="http://meta.wikimedia.org/wiki/Help:Special_characters#Displaying_Special_Characters">this page</a>
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for more details. For you lazy ones, this should work:</p>
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<pre>.Unicode {
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font-family: Code2000, "TITUS Cyberbit Basic", "Doulos SIL",
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"Chrysanthi Unicode", "Bitstream Cyberbit",
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"Bitstream CyberBase", Thryomanes, Gentium, GentiumAlt,
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"Lucida Grande", "Arial Unicode MS", "Microsoft Sans Serif",
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"Lucida Sans Unicode";
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font-family /**/:inherit; /* resets fonts for everyone but IE6 */
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}</pre>
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<p>The standard usage goes along the lines of <code><span class="Unicode">Crazy
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Unicode stuff here</span></code>. Characters in the
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<a href="http://en.wikipedia.org/wiki/Windows_Glyph_List_4">Windows Glyph List</a>
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usually don't need to be fixed, but for anything else you probably
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want to play it safe. Unless, of course, you don't care about IE6
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users.</p>
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<h3 id="migrate-variablewidth">Dealing with variable width in functions</h3>
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<p>When people claim that PHP6 will solve all our Unicode problems, they're
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misinformed. It will not fix any of the abovementioned troubles. It will,
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however, fix the problem we are about to discuss: processing UTF-8 text
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in PHP.</p>
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<p>PHP (as of PHP5) is blithely unaware of the existence of UTF-8 (with a few
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notable exceptions). Sometimes, this will cause problems, other times,
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this won't. So far, we've avoided discussing the architecture of
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UTF-8, so, we must first ask, what is UTF-8? Yes, it supports Unicode,
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and yes, it is variable width. Other traits:</p>
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<ul>
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<li>Every character's byte sequence is unique and will never be found
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inside the byte sequence of another character,</li>
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<li>UTF-8 may use up to four bytes to encode a character,</li>
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<li>UTF-8 text must be checked for well-formedness,</li>
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<li>Pure ASCII is also valid UTF-8, and</li>
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<li>Binary sorting will sort UTF-8 in the same order as Unicode.</li>
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</ul>
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<p>Each of these traits affect different domains of text processing
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in different ways. It is beyond the scope of this document to explain
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what precisely these implications are. PHPWact provides
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a very good <a href="http://www.phpwact.org/php/i18n/utf-8">reference document</a>
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on what to expect from each functions, although coverage is spotty in
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some areas. Their more general notes on
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<a href="http://www.phpwact.org/php/i18n/charsets">character sets</a>
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are also worth looking at for information on UTF-8. Some rules of thumb
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when dealing with Unicode text:</p>
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<ul>
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<li>Do not EVER use functions that:<ul>
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<li>...convert case (strtolower, strtoupper, ucfirst, ucwords)</li>
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<li>...claim to be case-insensitive (str_ireplace, stristr, strcasecmp)</li>
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</ul></li>
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<li>Think twice before using functions that:<ul>
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<li>...count characters (strlen will return bytes, not characters;
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str_split and word_wrap may corrupt)</li>
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<li>...entity-ize things (UTF-8 doesn't need entities)</li>
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<li>...do very complex string processing (*printf)</li>
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</ul></li>
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</ul>
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<p>...and always think in bytes, not characters. If you use strpos()
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to find the position of a character, it will be in bytes, but this
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usually won't matter since substr() also operates with byte indices!</p>
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<p>You'll also need to make sure your UTF-8 is well-formed and will
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probably need replacements for some of these functions. I recommend
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using Harry Fuecks' <a href="http://phputf8.sourceforge.net/">PHP
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UTF-8</a> library, rather than use mb_string directly. HTML Purifier
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also defines a few useful UTF-8 compatible functions: check out
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<code>Encoder.php</code> in the <code>/library/HTMLPurifier/</code>
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directory.</p>
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<h2 id="externallinks">Further Reading</h2>
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<p>Well, that's it. Hopefully this document has served as a very
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practical springboard into knowledge of how UTF-8 works. You may have
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decided that you don't want to migrate yet: that's fine, just know
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what will happen to your output and what bug reports you may recieve.</p>
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<p>Many other developers have already discussed the subject of Unicode,
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UTF-8 and internationalization, and I would like to defer to them for
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a more in-depth look into character sets and encodings.</p>
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@ -42,3 +42,7 @@ blockquote .label {font-weight:bold; font-size:1em; margin:0 0 .1em;
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/* Contains, without exception, $Id$, for SVN version info. */
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#version {text-align:right; font-style:italic; margin:2em 0;}
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#toc ol ol {list-style-type:lower-roman;}
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#toc ol {list-style-type:decimal;}
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#toc {list-style-type:upper-alpha;}
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