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[css2] Changed to section on conformance and and error handling. New conformance criteria
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‎css2/conform.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: conform.src,v 1.26 1997-11-25 00:04:49 ian Exp $ -->
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<!-- $Id: conform.src,v 1.27 1997-11-25 23:44:06 ian 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>Conformance: requirements and recommendations</TITLE>
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<LINK rel="next" href="process.html">
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<LINK rel="next" href="syndata.html">
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<LINK rel="previous" href="intro.html">
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<LINK rel="STYLESHEET" href="style/default.css" type="text/css">
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</HEAD>
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<BODY>
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<H1 align="center">Conformance: requirements and recommendations</H1>
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<H1 align="center">Conformance: Requirements and Recommendations</H1>
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<H2>Definitions</H2>
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href="#author">author</a>, <a href="#user">user</a>, and <a
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href="#user-agent">user agent</a>. The interaction of these sources is
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described in the section on <a href="cascade.html">cascading and
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inheritance</a>.
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inheritance</a>.</P>
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<dt><dfn><strong><a name="valid-style-sheet">Valid style sheet</a></strong></dfn></dt>
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<dd>The <span class="index-def" title="valid style sheet">validity</span>
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href="grammar.html">grammar of CSS2</a> and the <a
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href="selector.html">selector syntax</a>. Furthermore, it must only
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contain at-rules, property names, and property values defined in this
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specification.
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specification.</P>
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<dt><dfn><strong>Source document</strong></dfn>
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<dd>The document to which one or more style sheets refer.
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<dd>The document to which one or more style sheets refer.</dd>
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<dt><dfn><strong><a name="doclanguage">Document language</a></strong></dfn>
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<dd>The computer language of the source
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<span class="index-def" title="inline element"><em>Inline
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elements</em></span> are those elements of the document language that
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do not cause paragraph breaks (e.g., pieces of text, inline images,
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etc.)
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etc.)</P>
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<dt><dfn><strong><a name="doctree">Document tree</a></strong></dfn></dt>
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<dd>User agents transform a document written in the document language
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into a <dfn>document tree</dfn> where every element except one has
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exactly one <span class="index-def" title="parent">parent</span>
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element. (See the SGML (<a href="refs.html#ref-ISO8879"
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class="normref">[ISO8879]</a>) and XML (<a href="refs.html#ref-XML"
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class="normref">[XML]</a>) specifications for the definition of
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parent.) The one exception is the <span class="index-def"
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title="root">root</span> element, which has no parent. An element A is
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called a <span class="index-def" title="child">child</span> of an
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element B, if and only if B is the parent of A.
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<P>An element A is called an <span class="index-def"
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title="ancestor">ancestor</span> of an element B, if either (1) A is
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the parent B, or (2) A is the parent of some element C that is an
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ancestor of B.
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<P>An element A is called a <span class="index-def"
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title="descendant">descendant</span> of an element B, if and only if B
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is an ancestor of A.
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<P>An element A is called a <span class="index-def"
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title="sibling">sibling</span> of an element B, if and only if B and A
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share the same parent element. Element A is a preceding sibling if it
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comes before B in the document tree. Element B is a following sibling
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if it comes after B in the document tree.
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<div class="example"><P>
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For example, the following HTML document:
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<PRE>
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&lt;HTML&gt;
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&lt;TITLE&gt;My home page&lt;/TITLE&gt;
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&lt;BODY&gt;
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&lt;H1&gt;My home page&lt;/H1&gt;
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&lt;P&gt;Welcome to my home page! Let me tell you about my favorite
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composers:
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&lt;UL&gt;
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&lt;LI&gt; Elvis Costello
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&lt;LI&gt; Johannes Brahms
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&lt;LI&gt; Georges Brassens
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&lt;/UL&gt;
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&lt;/BODY&gt;
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&lt;/HTML&gt;
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</PRE>
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<P>results in the following tree:</P>
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<IMG src="images/doctree.gif" alt="Sample document tree">
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<P>According to the definition of HTML, HEAD elements will be inferred
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during parsing and become part of the document tree even if the HEAD
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tags are not in the document source.
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</div>
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</dd>
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<dt><dfn><strong><a name="author">Author</a></strong></dfn>
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<dd>An author is a person or program that
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writes or generates style sheets.
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writes or generates style sheets.</dd>
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<dt><dfn><strong><a name="user">User</a></strong></dfn>
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<dd>A user is a person who interacts with a user agent to view, hear,
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or otherwise use a document and its associated style sheets.
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or otherwise use a document and its associated style sheets.</dd>
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<dt><dfn><strong>User agent</strong></dfn>
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<dd>A <span class="index-def" title="user agent|UA"><em>user
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agent</em></span> is any program that interprets a document written in
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<dd>A <span class="index-def" title="user agent|UA">user
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agent</span> is any program that interprets a document written in
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the document language and applies associated style sheets by according
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to the terms of this specification. A user agent may display a
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document, read it aloud, cause it to be printed, convert it
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to another format, etc.
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to another format, etc.</dd>
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</dl>
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<dt><dfn><strong>Conforming user agent</strong></dfn>
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<dd>
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<p><em>This section defines <span class="index-def"
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title="conformance"><em>conformance</em></span> with the CSS2
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<h2><a name="conformance">Conformance</a></h2>
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<P>This section defines <span class="index-def"
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title="conformance">conformance</span> with the CSS2
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specification only. There may be other levels of CSS in the future
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that may require a UA to implement a different set of features in
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order to conform.</em></P>
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that may require a user agent to implement a different set of features
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in order to conform.
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<P>In general, the following points must be observed by user agents
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claiming conformance to this specification:</P>
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<ol>
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<li>It must define the <a href="media.html">media types</a> it
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supports in terms of CSS media types.
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<li>It must define the CSS2 <a href="media.html">media types</a> it
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supports.
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<li>For each source document, it must retrieve all
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associated style sheets that are appropriate for the supported media
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types.
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<li>It must parse the style sheets according to this specification.
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In particular, it must recognize all at-rules, blocks, declarations,
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and selectors (see the <a href="grammar.html">grammar of CSS2</a>).
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If a user agent encounters a property relative to a supported
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medium, the user agent must parse the value according to the property
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If a user agent encounters a property relevant to a supported
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media type, the user agent must parse the value according to the property
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definition. This means that the user agent must accept all legal
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values and must reject other values. User agents may skip values of
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properties relative to unsupported <a href="media.html">media
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properties relevant to unsupported <a href="media.html">media
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types</a>.
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<li>Given a <a href="#doctree">document tree</a>, it must
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assign a value for every supported property according to
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<P>Not every user agent must observe every point, however:
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<ul>
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<li>A user agent that only <em>inputs</em> style sheets must
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only respect points 1 - 3.
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<li>A user agent that <em>inputs</em> style sheets must
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respect points 1 - 3.
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<li>A user agent that only <em>outputs</em> style sheets is only required
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<li>A user agent that <em>outputs</em> style sheets is only required
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to output <a href="#valid-style-sheet">valid style sheets</a>
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<li>A user agent that <em>renders</em> a document with associated style
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user agent cannot render colors on a monochrome monitor or a black and
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white page) does not imply non-conformance. </P>
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<p>This specification also recommends that a UA offer the following
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<p>This specification also recommends that a user agent offer the following
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functionality to the user (these do not refer to any specific
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user interface):
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them in strict accordance with this specification.
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</UL>
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<P>Different user interface paradigms may have their own constraints:
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a VR browser may rescale the document based on its "distance" from the
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user.</P>
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<h2>Error conditions</h2>
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<P> UAs may offer readers additional choices on presentation. For
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example, the UA may provide options for readers with visual
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impairments or may provide the choice to disable blinking.</P>
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<P>In general, this document does not specify error
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handling behavior for user agents.
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<dt><dfn><strong>Error conditions</strong></dfn>
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<dd>This specification does not define how conforming user agents
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handle general error conditions, including how user agents
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behave when they encounter elements,
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attributes, attribute values, or
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entities not specified in this document.
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<P>However, user agents must observe the <a
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href="parsing-errors">rules for handling parsing errors</a>.
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<P>Since user agents may vary in how they handle error conditions,
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authors and users must not rely on specific error recovery behavior.
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</dl>
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</BODY>
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</html>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml

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