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[css2] Proposed text about BOMs
--HG-- extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%402194
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‎css2/refs.src‎

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<html lang="en">
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<!-- $Id: refs.src,v 2.22 2003-09-05 14:25:56 bbos Exp $ -->
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<!-- $Id: refs.src,v 2.23 2003-12-05 18:25:10 bbos Exp $ -->
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<HEAD>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<TITLE>Bibliography</TITLE>
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<dd>"Uniform Resource Locators", T. Berners-Lee, L. Masinter, and M. McCahill, December 1994.<BR>
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Available at <a href="http://www.ietf.org/rfc/rfc1738.txt">http://www.ietf.org/rfc/rfc1738.txt</a>.
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<dt><strong><a name="ref-RFC2781" class="normref">[RFC2781]</a></strong>
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<dd>"UTF-16, an encoding of ISO 10646", P. Hoffman, F. Yergeau, February 2000<br>
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Available at <a href="http://www.ietf.org/rfc/rfc2781.txt">http://www.ietf.org/rfc/rfc2781.txt</a>.
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<dt><strong><a name="ref-SRGB" class="normref">[SRGB]</a></strong>
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<dd>"Proposal for a Standard Color Space for the Internet - sRGB",
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M. Anderson, R. Motta, S. Chandrasekar, M. Stokes.<BR>

‎css2/syndata.src‎

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
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"http://www.w3.org/TR/1998/REC-html40-19980424/loose.dtd">
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<html lang="en">
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<!-- $Id: syndata.src,v 2.90 2003-12-01 16:11:33 bbos Exp $ -->
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<!-- $Id: syndata.src,v 2.91 2003-12-05 18:25:10 bbos Exp $ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Syntax and basic data types</title>
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<li>Mechanisms of the language of the
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referencing document (e.g., in HTML, the "charset"
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attribute of the LINK element).</li>
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<li>UA-dependent mechanisms</li>
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<li>UA-dependent mechanisms <ins>(e.g., guessing based on the <a
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href="#BOM">BOM</a>)</ins></li>
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</ol>
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<p><ins cite="http://www.damowmow.com/temp/csswg/css21/issues"
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title="issue 44">[A BOM character is ignored if it conflicts, otherwise used]</ins>
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<del>
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<p>At most one @charset rule may appear in an external
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style sheet &mdash; it must <em>not</em> appear in an embedded style sheet
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&mdash; and it must appear at the very start of the document, not preceded
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by any characters. After "@charset", authors specify the name of a
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character encoding. The name must be a charset name as described in
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the IANA registry (See [[IANA]]. Also, see [[-CHARSETS]] for a complete
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list of charsets). For example:
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</p>
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<p>At most one @charset rule may appear in an external style sheet
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&mdash; it must <em>not</em> appear in an embedded style sheet &mdash;
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and it must appear at the very start of the document, not preceded by
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any characters.
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<div class="example"><p>
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@charset "ISO-8859-1";
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</p></div>
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</del>
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<ins>
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<p>At most one @charset rule may appear in an external style sheet and
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it must appear at the very start of the document, not preceded by any
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characters, except possibly a <a href="#BOM">"BOM" (see below)</a>.
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Any other @charset rules must be ignored by the UA.
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</ins>
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<p>After "@charset", authors specify the name of a character encoding.
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The name must be a charset name as described in the IANA registry (See
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[[IANA]]. Also, see [[-CHARSETS]] for a complete list of charsets).
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For example:
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<pre class="example">@charset "ISO-8859-1";</pre>
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<p>This specification does not mandate which character encodings
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a user agent must support.
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</p>
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<p>Note that reliance on the @charset construct theoretically poses a
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<ins cite="http://www.damowmow.com/temp/csswg/css21/issues"
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title="issue 44">
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<p id="BOM">If an external style sheet has U+FEFF ("zero width
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non-breaking space") as the first character (i.e., even before any
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@charset rule), this character is interpreted as a so-called "Byte
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Order Mark" (BOM), as follows:
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<ul>
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<li>If the style sheet is encoded as "UTF-16" [[RFC2781]] or "UTF-32"
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[[UNICODE]], the BOM determines the byte order ("big-endian" or
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"little-endian") as explained in the cited RFC.
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<li>If the style sheet is encoded as anything else, the U+FEFF
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character is ignored.
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</ul>
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<p>An external style sheet <em>should</em> start with a BOM if it is
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encoded as "UTF-16" or "UTF-32" and <em>should not</em> have a BOM in
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any other encodings.
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<p class="note">Note that the BOM can only be ignored if it agrees
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with the encoding. E.g., if a style sheet encoded as "UTF-8" starts
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with 0xEF 0xBB 0xBF those three bytes are ignored, since they
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correctly encode the character U+FEFF in UTF-8. But if a style sheet
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encoded as "ISO-8859-1" starts with the two bytes 0xFE 0xFF (the BOM
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for big-endian UTF-16), the two bytes are simply interpreted as the
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two characters "�" and "�".
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</ins>
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<p class="note">Note that reliance on the @charset construct
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theoretically poses a
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problem since there is no <em>a priori</em> information on how it is
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encoded. In practice, however, the encodings in wide use on the
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Internet are either based on ASCII, UTF-16, UCS-4, or (rarely) on

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