8000 [css2] Added definition of "document tree", "parent", etc. · w3c/csswg-drafts@b20ad26 · GitHub
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[css2] Added definition of "document tree", "parent", etc.
(See http://lists.w3.org/Archives/Member/w3c-css-wg/1997OctDec/0014.html) --HG-- extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%40223
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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 1.17 1997-10-03 22:12:36 ian Exp $ -->
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<!-- $Id: conform.src,v 1.18 1997-10-09 14:41:20 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>Definitions and document conventions</TITLE>
@@ -24,11 +24,26 @@ include "P" (for structuring paragraphs), "TABLE" (for creating
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tables), "OL" (for creating ordered lists), etc.
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<H3><a name="doctree">Document tree</a></H3>
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<H3><a name="doctree">Document tree, parent, child, descendant,
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ancestor</a></H3>
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<P>When a document written in the document language is parsed by a user
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agent, the result is a <span class="index-def" title="document
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tree">document tree structure</span>.
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<P>CSS makes use of the fact that a document in the document language
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can be thought of as a tree: every element except one has exactly one
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<span class="index-def" title="parent">parent</span> element. (See the
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SGML and XML specifications[ref] for the definition of parent.) The one
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exception is the <span class="index-def" title="root">root</em>
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element, which has no parent. An element A is called a <span
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class="index-def" title="child">child</span> of an element B, if and
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only if B is the parent of A.
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<P>An element A is called a <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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<div class="example"><P>
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For example, the following HTML document:
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the list item text.
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-->
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<P>The <span class="index-def" title="root element"><em>root
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element</em></span> of a document is the element at the top of the
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document tree.
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<H3><span class="index-def" title="inheritance">Inheritance of
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property values</span></H3>
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<H3><span class="index-def" title="inheritance">Inheritance</span></H3>
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<P>CSS works, basically, by converting the document tree to a tree of
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rendering objects that are characterized by properties. A property has
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a name, such as 'font-weight' and a value, for example 'bold'. All
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rendering objects have the same properties, but the values may
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differ. The values can be set explicitly, but if they are not, the
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values are either inherited, or set to an "initial" value.
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<P>Elements inherit some property values from their ancestors in the
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document tree.
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<P>If a value is inherited, it means the value is the same as the
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value in the rendering object for the parent element.
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<div class="example"><P>
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Suppose there is an H1 element with an emphasized element inside:
@@ -79,21 +98,22 @@ Suppose there is an H1 element with an emphasized element inside:
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&lt;H1&gt;The headline &lt;EM&gt;is&lt;/EM&gt; important!&lt;/H1&gt;
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</PRE>
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<P> If no color has been assigned to the EM element, the emphasized
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"is" will inherit the color of the parent element, i.e., it will also
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appear in blue.
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<P>If no color has been assigned to the EM element, the emphasized
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"is" will inherit the color of the parent element, so if H1 has the
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color blue, the EM element will likewise be in blue.
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</div>
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<!--
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<P>Other style properties are likewise inherited, e.g., <span
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class="propinst-font-family">'font-family'</span> and <span
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class="propinst-font-size">'font-size'</span>.
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-->
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<P> To set a "default" style property for a document, one can set the
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property on the root of the document tree. In HTML, the HTML or BODY
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elements can serve this function. This will work even if the author
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omits the BODY tag in the HTML source since the HTML parser will
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infer the missing tag.
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elements can serve this function. Note that this will work even if the
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author omits the BODY tag in the HTML source since the HTML parser
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will infer the missing tag.
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<div class="example"><P>
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<P> Not all style properties are inherited. For example, the <span
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class="propinst-background">'background'</span> property is not
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inherited. However, by default, when an element has no explicit
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background, its parent's background shines through.
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inherited. (However, by default, when an element has no explicit
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background, its parent's background shines through.) All properties
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have an initial value. If the property is not inherited, the value
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will be the initial value.
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Thus, in the example above, the <span
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<!--
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<P>Thus, in the example above, the <span
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class="propinst-background">'background'</span> property on the BODY
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element, although not inherited, establishes the background of the
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entire document. The background will be white if the image is not
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available (see the section on <a href="./colors.html#backgrounds">
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backgrounds</a> for more information).
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-->
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<P>Each property definition indicates whether the property is
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inherited by child elements.
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inherited by child elements, and what the initial value of the
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property is.
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<P>The root element obviously can't inherit values. If no value is set
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explicitly, the initial value will be used.
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<P>For all inherited CSS2 properties, if the value is specified as a
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percentage, child elements inherit the resultant value, not the
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percentage value.
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<div class="example"><P>
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For example, with the style sheet
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<pre>
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BODY {font-size: 10pt}
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H1 {font-size: 120%}
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</pre>
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<p>and the document fragment
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<pre>
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&lt;BODY>
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&lt;H1>A &lt;EM>large&lt;/EM> heading&lt;/H1>
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...
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</pre>
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<p>the H1 will have <span
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class="prop-inst-font-size">'font-size'</span> 12pt (120% times 10pt),
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but the EM will also be 12pt, since it inherits the resultant value
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(12pt), not the percentage (120%).
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</div>
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<P>When a percentage value is set on a property of the root element,
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and the percentage is defined as referring to the inherited value of
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some property X, the resultant value is the percentage times the
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initial value of property X.
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<div class="example"><P>
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For example, with and HTML document and the style sheet
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<pre>
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HTML {font-size: 120%}
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</pre>
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<p>The resultant value for <span
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class="prop-inst-font-size">'font-size'</span> will be 120% of the
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initial value of the 'font-size' property. (The initial value of
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'font-size' is defined to be 'medium', so the resultant value is 20%
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larger than 'medium'.)
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</div>
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<H3><span class="index-def" title="user agent|UA">User
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agent</span> (or UA)</H3>
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<H3><span class="index-def" title="default style sheet">Default style
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sheet</span></H3>
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<P>When a document has no associated style sheets, user agents apply
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<P>A user agent can provide a default style sheet, so that even
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when a document has no associated style sheets, user agents apply
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rules from their default style sheet for presenting the document. A
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user agent's default style sheet generally presents elements of the
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document language in ways that satisfy the expectations that most people
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have (e.g., for visual browsers, the EM element in HTML is presented
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using an italic font). The default style sheet is considered along
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with author and user style sheets when determining how rules <a
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href="cascade.html">cascade</a>.
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using an italic font).
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<P>If a document has associated style sheets, the default style sheet
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is considered along with author and user style sheets when determining
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how rules <a href="cascade.html">cascade</a>.
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<P>User agents that don't actually use style sheets to specify default
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rules must behave as if they did.
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<P>See <a href="sample.html">"A sample style sheet for HTML 2.0"</a>
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for a recommended default style sheet for HTML 4.0 documents.
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<H3><span class="index-def" title="visual rendering model">Visual
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rendering model</span></H3> The <a href="./flowobj.html">visual
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rendering model</a> describes how user agents should format a stream
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<li> non-terminals that have the same range of values as a property
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bearing the same name (e.g., &lt;border-width&gt;
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&lt;background-attachment&gt;, etc.). In this case, the non-terminal
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names is the property name (complete with quotes) between "&lt;" and
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name is the property name (complete with quotes) between "&lt;" and
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"&gt;" (e.g., &lt;'border-width'&gt;). In the electronic version of
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the document, each instance of this type of non-terminal links to the
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corresponding property definition.
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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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sgml-declaration:"~/SGML/HTML4.decl"
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sgml-default-doctype-name:"html"
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sgml-minimize-attributes:t
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sgml-nofill-elements:("pre" "style" "br")
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sgml-live-element-indicator:t
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End:
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-->

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