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<!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN' 'http://www.w3.org/TR/html4/strict.dtd'>
<html lang="en">
<head profile="http://www.w3.org/2006/03/hcard">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>CSS Exclusions and Shapes Module Level 3</title>
<link rel="stylesheet" type="text/css" href="../shared/style/default.css" />
<script src='https://test.csswg.org/harness/annotate.js#CSS3-EXCLUSIONS_DEV' type='text/javascript' defer></script>
<style type="text/css">
.singleImgExample {
display: block;
margin: auto;
}
.example-table {
table-layout: fixed;
width: 100%;
}
.example-table tr td img {
width: 90%;
}
</style>
<link rel="stylesheet" type="text/css"
href="https://www.w3.org/StyleSheets/TR/W3C-ED.css">
<link rel="stylesheet" type="text/css"
href="../shared/style/issues.css">
<link id="st" href="../shared/style/alternate-spec-style.css" rel="stylesheet"
type="text/css" title="alternate spec style">
</head>
<body>
<div id="div-head" class="head">
<p><a href="http://www.w3.org/"><img id="mobile-logo" alt="W3C" height="53" src=
"https://www.w3.org/2008/site/images/logo-w3c-mobile-lg" width="90"></a>
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"https://www.w3.org/Icons/w3c_home" width="72"></a> <!--end-logo--></p>
<h1 id="css-exclusions-module">CSS Exclusions and Shapes Module Level 3</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:</dt>
<dd><a href="https://drafts.csswg.org/css3-exclusions/">https://drafts.csswg.org/css3-exclusions/</a></dd>
<!--<dd><a href="[VERSION]">https://www.w3.org/TR/[YEAR]/WD-css3-exclusions-[CDATE]/</a></dd>-->
<dt>Latest version:</dt>
<dd><a href="https://www.w3.org/TR/[SHORTNAME]/">https://www.w3.org/TR/[SHORTNAME]/</a></dd>
<dt>Editor's Draft:</dt>
<dd><a href="https://drafts.csswg.org/[SHORTNAME]/">https://drafts.csswg.org/[SHORTNAME]/</a>
<dt>Previous version:</dt>
<dd>None</dd>
<dt>Editors:</dt>
<dd class="vcard"><span class="fn">Vincent Hardy</span>, <span class="org">Adobe Systems, Inc.</span>, <span class="email">vhardy@adobe.com</span></dd>
<dd class="vcard"><span class="fn">Rossen Atanassov</span>, <span class="org">Microsoft Corporation</span>, <span class="email">ratan@microsoft.com</span></dd>
<dd class="vcard"><span class="fn">Alan Stearns</span>, <span class="org">Adobe Systems, Inc.</span>, <span class="email">stearns@adobe.com</span></dd>
<dt>Issues List:</dt>
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Exclusions&resolution=---&cmdtype=doit">in Bugzilla</a></dd>
<dt>Feedback:</dt>
<dd><a href="mailto:www-style@w3.org?subject=%5B[css-exclusions]%5D%20feedback"
>www-style@w3.org</a>
with subject line “<kbd>[css-exclusions]
<var>… message topic …</var></kbd>”
(<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/"
>archives</a>)
</dl>
<!--copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>
CSS Exclusions define arbitrary areas around which <a href="https://www.w3.org/TR/CSS2/visuren.html#inline-boxes">inline content</a> ([[!CSS21]]) content can flow.
CSS Exclusions can be defined on any CSS block-level elements. CSS
Exclusions extend the notion of content wrapping previously limited to
floats.</p>
<p>CSS Shapes control the geometric shapes used for wrapping inline flow
content outside or inside an element. CSS Shapes can be applied to any
element. A circle shape on a float will cause inline content to wrap around
the circle shape instead of the float's bounding box.</p>
<p>Combining CSS Exclusions and CSS Shapes allows sophisticated layouts,
allowing interactions between shapes in complex positioning schemes.</p>
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--status-->
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--toc-->
<h2 id="intro">Introduction</h2>
<p><em>This section is not normative.</em></p>
<p>
The exclusions section of this specification defines features that allow inline flow
content to wrap around outside the <span>exclusion area</span> of elements.
</p>
<p>
The shapes section of the specification defines properties to control the geometry of
an element's <span>exclusion area</span> as well as the geometry used for wrapping
an element's inline flow content.
</p>
<h2 id="definitions">Definitions</h2>
<dfn>Exclusion box</dfn>
<p>
A <a href="https://www.w3.org/TR/css3-box/">box</a> ([[!CSS3BOX]]) that defines an <span>exclusion area</span> for other boxes. The 'wrap-flow'
property is used to make an element's generated box an exclusion box. An exclusion box contributes
its <span>exclusion area</span> to its <a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">
containing block's</a> <span>wrapping context</span>. An element with a 'float'
computed value other than 'none' does not become an exclusion.
</p>
<dfn>Exclusion area</dfn>
<p>
The area used for excluding inline flow content around an exclusion box. The
<span>exclusion area</span> is equivalent to the <a href="https://www.w3.org/TR/CSS2/box.html#box-dimensions">
border box</a> for an exclusion box.
This specification's
'shape-outside' property
can be used to define arbitrary,
non-rectangular <span>exclusion areas</span>.
The 'shape-inside' property also defines an <span>exclusion area</span>,
but in this case it is the area outside the shape that inline content avoids.
</p>
<dfn>Float area</dfn>
<p>
The area used for excluding inline flow content around a float element. By default, the
float area is the float element's
<a href="https://www.w3.org/TR/CSS2/box.html#box-dimensions">margin box</a>.
This specification's
'shape-outside' property can be used to define arbitrary, non-rectangular float
areas.
</p>
<dfn>Exclusion element</dfn>
<p>An block-level element which is not a float and generates an <span>exclusion box</span>.
An element generates an exclusion box when its 'wrap-flow' property's computed value is not 'auto'.
</p>
<dfn>Wrapping context</dfn>
<div class="issue-marker" data-bug_id="15086" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15086">Issue-15086</a>
<div class="issue-details">
<p class="short-desc">should the wrapping context be generic and include floats?</p>
</div>
</div>
<p>
The <span>wrapping context</span> of a box is a collection of <span>exclusion areas</span>
contributed by its associated <span>exclusion boxes</span> and elements with 'shape-inside'. During layout,
a box wraps its inline flow content in the <code>wrapping area</code> that corresponds to the subtraction of
its <span>wrapping context</span> from its own &
D4C
lt;span>content area</span>.
</p>
<p>
A box inherits its
<a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">containing block's</a>
<span>wrapping context</span> unless it specifically
resets it using the 'wrap-through' property.
</p>
<dfn>Content area</dfn>
<p>
The <a href="https://www.w3.org/TR/CSS2/box.html#box-dimensions">content area</a>
is normally used for layout of the inline flow content of a box.
</p>
<dfn>Wrapping area</dfn>
<p>
The area used for layout of inline flow content of a box affected by a <span>wrapping context</span>, defined by subtracting the <span>wrapping context</span> from its <span>content area</span>
</p>
<div class="issue-marker" data-bug_id="15089" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15089">Issue-15089</a>
<div class="issue-details">
<p class="short-desc">shrink-to-fit circle / shape</p>
</div>
</div>
<dfn title="outside-inside">Outside and inside</dfn>
<p>
In this specification, 'outside' refers to DOM content that is not a descendant of an element
while 'inside' refers to the element's descendants.
</p>
<h2 id="exclusions">Exclusions</h2>
<p>
Exclusion elements define <span>exclusion areas</span> that contribute to their containing block's
<span>wrapping context</span>. As a consequence, exclusions impact the layout of their
containing block's descendants.
<p>
<p>
Elements layout their inline content in their <span>content area</span> and wrap around the
<span>exclusion areas</span> in their associated <span>wrapping context</span>. If the element is itself an exclusion, it
does not wrap around its own exclusion shape and the impact of other exclusions on other
exclusions is controlled by the 'z-index' property as explained in the
<a href="#exclusions-order">exclusions order</a> section.
</p>
The <a href="#shapes">shape properties</a> can be used to change the shape of
<span>exclusion areas</span>.
</p>
<h3 id="declaring-exclusions">Declaring exclusions</h3>
<p>
An element becomes an exclusion when its 'wrap-flow' property has a computed value other than
'auto'.
</p>
<h4 id="wrap-flow-property">The 'wrap-flow' property</h4>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn title="'wrap-flow'">wrap-flow</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var>auto</var> | <var>both</var> | <var>start</var> | <var>end</var> | <var>minimum</var> | <var>maximum</var> | <var>clear</var></td>
</tr>
<tr>
<th>Initial:</th>
<td>auto</td>
</tr>
<tr>
<th>Applies to:</th>
<td>block-level elements.</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified except for element's whose 'float' computed value is not
<code class="css">none</code>, in which case the computed value is 'auto'.</td>
</tr>
</table>
<p>The values of this property have the following meanings:</p>
<dl>
<dt><dfn title="'wrap-flow'!!'auto'">auto</dfn></dt>
<dd>
No exclusion is created. Inline flow content interacts with the element as usual.
In particular, if the element is a
<a href="https://www.w3.org/TR/CSS2/visuren.html#floats">float</a> (see [[CSS21]]), the
behavior is unchanged.
</dd>
<dt><dfn title="'wrap-flow'!!'both'">both</dfn></dt>
<dd>
Inline flow content can flow on all sides of the exclusion.
</dd>
<dt><dfn title="'wrap-flow'!!'start'">start</dfn></dt>
<dd>
Inline flow content can flow
around the start edge
of the <span>exclusion area</span>
but must leave the area
next to the end edge
of the exclusion empty.
</dd>
<dt><dfn title="'wrap-flow'!!'end'">end</dfn></dt>
<dd>
Inline flow content can flow
around the end edge
of the <span>exclusion area</span>
but must leave the area
next to the start edge
of the exclusion empty.
</dd>
<dt><dfn title="'wrap-flow'!!'minimum'">minimum</dfn></dt>
<dd>
Inline flow content can flow
around the edge of the exclusion
with the smallest available space
within the flow content's containing block,
and must leave the other edge
of the exclusion empty.
</dd>
<dt><dfn title="'wrap-flow'!!'maximum'">maximum</dfn></dt>
<dd>
Inline flow content can flow
around the edge of the exclusion
with the largest available space
within the flow content's containing block,
and must leave the other edge
of the exclusion empty.
</dd>
<dt><dfn title="'wrap-flow'!!'clear'">clear</dfn></dt>
<dd>
Inline flow content can only flow
before and after the exclusion
in the flow content's block direction
and must leave the areas
next to the start and end edges
of the exclusion empty.
</dd>
</dl>
<p>
If the property's computed value is 'auto', the element does not become an
<span>exclusion</span>.
</p>
<p>
Otherwise, a computed 'wrap-flow' property value of 'both', 'start', 'end', 'minimum',
'maximum' or 'clear' on an element makes that element an <span>exclusion element</a>.
It's <span>exclusion shape</span> is contributed to its containing block's
<span>wrapping context</span>, causing the containing block's descendants to wrap around
its <span>exclusion area</span>.
</p>
<div class="figure">
<img alt="LTR text wrapping on left edge, RTL text wrapping on right edge, and vertical text wrapping on top edge." src="images/exclusion-writing-modes.png" width="70%" />
<p class="caption">Exclusion with 'wrap-flow: start' interacting with various writing modes.</p>
</div>
<p>Determining the relevant edges of the exclusion depends on the <a href="https://www.w3.org/TR/css3-writing-modes/#text-flow">writing mode</a> [[!CSS3-WRITING-MODES]] of the content wrapping around the <span>exclusion area</span>.
<p>An <span>exclusion element</span> establishes a
new <a href="">block formatting context</a> (see [[!CSS21]]) for its content.</p>
<div class="figure">
<img alt="General illustration showing how exclusions combine" src="images/exclusions-illustration.png" width="70%" />
<p class="caption">Combining exclusions</p>
</div>
<p>
The above figure illustrates how exclusions are combined.
The outermost box represents an element's content box.
The A, B, C and D darker gray boxes represent exclusions
in the element's <span>wrapping context</span>.
A, B, C and D have their respective 'wrap-flow'
computed to 'both', 'start', 'end' and 'clear' respectively.
The lighter gray areas show the additional areas
that are excluded for inline layout
as a result of the 'wrap-flow'value.
For example, the area to the right of 'B'
cannot be used for inline layout
of left-to-right writing mode content
because the 'wrap-flow' for 'B' is 'start'.
</p>
<p>
The background 'blue' area shows what areas are available
for a left-to-right writing mode element's inline content layout.
All areas represented with a light or dark shade of gray
are not available for (left-to-right writing mode) inline content layout.
</p>
<div class="issue-marker wrapper">
<div class="issue-marker" data-bug_id="15084" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15084">Issue-15084</a>
<div class="issue-details">
<p class="short-desc">Fluidity of the layout with respect to different amounts of content</p>
</div>
</div>
</div>
<div class="example">
<p>
The 'wrap-flow' property values applied to exclusions as grid items.
</p>
<code class="html"><pre>
<div id="grid">
<div id="top-right" class="exclusion"></div>
<div id="bottom-left" class="exclusion"></div>
<div id="content">Lorem ipsum…</div>
</div>
<style type="text/css">
#grid {
width: 30em;
height: 30em;
display: grid;
grid-columns: 25% 25% 25% 25%;
grid-rows: 25% 25% 25% 25%;
#top-right {
grid-column: 3;
grid-row: 2;
}
#bottom-left {
grid-column: 2;
grid-row: 3;
}
.exclusion {
wrap-flow: <see below>
}
#content {
grid-row: 1;
grid-row-span: 4;
grid-column: 1;
grid-column-span: 4;
}
</style>
</pre></code>
<p>The following figures illustrate the visual rendering for different values
of the 'wrap-flow' property. The gray grid lines are marking the grid cells. and the
blue area is the exclusion box (positioned by the grid).</p>
<table class="example-table">
<tr>
<td><code class="html">.exclusion{ wrap-flow: auto; }</code></td>
<td><code class="html">.exclusion{ wrap-flow: both; }</code></td>
</tr>
<tr>
<td><img src="images/exclusion_wrap_side_auto.png" alt="Example rendering for wrap-side: auto" /></td>
<td><img src="images/exclusion_wrap_side_both.png" alt="Example rendering for wrap-side: both" /></td>
</tr>
<tr>
<td><code class="html">.exclusion{ wrap-flow: start; }</code></td>
<td><code class="html">.exclusion{ wrap-flow: end; }</code></td>
</tr>
<tr>
<td><img src="images/exclusion_wrap_side_left.png" alt="Example rendering for wrap-side: start" /></td>
<td><img src="images/exclusion_wrap_side_right.png" alt="Example rendering for wrap-side: end" /></td>
</tr>
<tr>
<td><code class="html">.exclusion{ wrap-flow: minimum; }</code></td>
<td><code class="html">.exclusion{ wrap-flow: maximum; }</code></td>
</tr>
<tr>
<td><img src="images/exclusion_wrap_side_minimum.png" alt="Example rendering for wrap-side: minimum" /></td>
<td><img src="images/exclusion_wrap_side_maximum.png" alt="Example rendering for wrap-side: maximum" /></td>
</tr>
<tr>
<td><code class="html">.exclusion{ wrap-flow: clear; }</code></td>
<td></td>
</tr>
<tr>
<td><img src="images/exclusion_wrap_side_clear.png" alt="Example rendering for wrap-side: clear" /></td>
<td></td>
</tr>
</table>
</div>
<!-- End section "wrap-flow Property" -->
<!-- End section "Declaring Exclusions" -->
<h3 id="scope-and-effect-of-exclusions">Scope and effect of exclusions</h3>
<p>
An <span>exclusion</span> affects
the inline flow content descended
from the exclusion's containing block
(defined in <a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">
CSS 2.1 10.1</a>)
and that of all descendant elements
of the same containing block.
All inline flow content
inside the containing block
of the exclusions is affected.
To stop the effect of exclusions
defined outside an element,
the 'wrap-through' property can be used
(see the <a href="#propagation-of-exclusions">propagation of exclusions</a>
section below).
</p>
<p>
As a reminder,
for exclusions with 'position:fixed',
the containing block is that
of the root element.
</p>
<!-- End section "Scope and Effect of Exclusions" -->
<h3 id="propagation-of-exclusions">Propagation of Exclusions</h3>
<p>
By default, an element inherits its parent <span>wrapping context</span>. In other words
it is subject to the exclusions defined <span title="outside-inside">outside</sapn> the element.
</p>
<p>Setting the 'wrap-through' property to 'none' prevents an element from inheriting its parent
<span>wrapping context</span>. In other words, exclusions defined 'outside' the element, have not effect
on the element's children layout.
</p>
<div class="note">
Exclusions defined by an element's descendants still contribute to their containing block's
<span>wrapping context</span>. If that containing block is a child of an element with 'wrap-through'
computes to none, or the element itself, then exclusion still have an effect on the children of that
containing block element.
</div>
<h4 id="wrap-through-property">The 'wrap-through' Property</h4>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn title="'wrap-through'">wrap-through</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var>wrap</var> | <var>none</var></td>
</tr>
<tr>
<th>Initial:</th>
<td>wrap</td>
</tr>
<tr>
<th>Applies to:</th>
<td>block-level elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified</td>
</tr>
</table>
<p>The values of this property have the following meanings:</p>
<dl>
<dt><dfn title="'wrap-through'!!'wrap'">wrap</dfn></dt>
<dd>
The element inherits its parent node's <span>wrapping context</span>. Its descendant
inline content wraps around exclusions defined <span title="outside-inside">outside</span>
the element.
</dd>
</dl>
<dl>
<dt><dfn title="'wrap-through'!!'none'">none</dfn></dt>
<dd>
The element does not inherit its parent node's <span>wrapping context</span>. Its
descendants are only subject to exclusion shapes defined <span title="outside-inside">inside</span>
the element.
</dd>
</dl>
<div class="example">
<p>
Using the 'wrap-through' property to control the effect of exclusions.
</p>
<pre><code class="html">
<style type="text/css">
#grid {
display: grid;
grid-columns: 25% 50% 25%;
grid-rows: 25% 25% 25% 25%;
}
#exclusion {
grid-row: 2;
grid-row-span: 2;
grid-column: 2;
wrap-flow: <see below>
}
#rowA, #rowB {
grid-row-span: 2;
grid-column: 1;
grid-column-span: 3;
}
#rowA {
grid-row: 1;
}
#rowB {
grid-row: 3;
}
</style>
<style type="text/css">
.exclusion {
wrap-flow: both;
position: absolute;
left: 20%;
top: 20%;
width: 50%;
height: 50%;
background-color: rgba(220, 230, 242, 0.5);
}
</style>
<div id="grid">
<div class=”exclusion”></div>
<div id="rowA" style=”wrap-through: wrap;”> Lorem ipsum dolor sit amet...</div>
<div id="rowB" style=”wrap-through: none;”> Lorem ipsum dolor sit amet...</div>
</div>
</code></pre>
<img class="singleImgExample" src="images/exclusion_wrap_through.png" alt="Example rendering of wrap-through: wrap | none" style="max-width:40%"/>
</div>
<!-- End section "wrap-through property" -->
<!-- removed as wrap-margin and wrap-padding changed to shape-margin and shape-padding
<h4 id="wrap-shorthand-property">The 'wrap' Shorthand Property</h4>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn title="'wrap'">wrap</dfn></td>
</tr>
<tr>
<th>Value:</th>
<td><var><wrap-flow></var> || <var><wrap-margin></var> [ / <var><wrap-padding></var>]</td>
</tr>
<tr>
<th>Initial:</th>
<td>see individual properties</td>
</tr>
<tr>
<th>Applies to:</th>
<td>block-level elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>no</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>see individual properties</td>
</tr>
</table>
<p>
The 'wrap' property is a shorthand property for setting the exclusions properties
at the same place in the style sheet.
</p>
-->
<!-- End section "wrap shorthand property" -->
<!-- End section "Propagation of Exclusions" -->
<h3 id="exclusions-order">Exclusions order</h3>
<p>
Exclusions follow the painting order (See [[!CSS21]] Appendix E). Exclusions are
applied in reverse to the document order in which they are defined. The last exclusion
appears on top of all other exclusion, thus it affects the inline flow content of
all other preceding exclusions or elements descendant of the same containing block.
The 'z-index' property can be used to change the ordering of
<a href="https://www.w3.org/TR/CSS2/visuren.html#choose-position">positioned</a> exclusion
boxes (see [[!CSS21]]). Statically positioned exclusions are not affected by the
'z-index' property and thus follow the painting order.
</p>
<div class="issue-marker" data-bug_id="16474" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=16474">Issue-16474</a>
<div class="issue-details">
<p class="short-desc">Improve Example 3 about exclusion order</p>
</div>
</div>
<div class="example">
<p>Ordering of exclusions.</p>
<pre><code class="html">
<style type="text/css">
.exclusion {
wrap-flow: both;
position: absolute;
width: 50%;
height: auto;
}
</style>
<div class=”exclusion” style=”top: 0px; left: 0px;”>
Lorem ipsum dolor sit amet...
</div>
<div id="orderedExclusion" class=”exclusion” style=”top: 25%; left: 25%;”>
Lorem ipsum dolor sit amet...
</div>
<div class=”exclusion” style=”top: 50%; left: 50%;”>
Lorem ipsum dolor sit amet...
</div>
</code></pre>
<table class="example-table">
<tr>
<td style="width:50%"><code class="html">#orderedExclusion{ z-index: auto; }</code></td>
<td style="width:50%"><code class="html">#orderedExclusion{ z-index: 1; }</code></td>
</tr>
<tr>
<td><img class="singleImgExample" src="images/exclusion_ordering.png" alt="Example rendering of default exclusion ordering." /></td>
<td><img class="singleImgExample" src="images/exclusion_ordering_z_order.png" alt="Example rendering of default exclusion ordering." /></td>
</tr>
</table>
</div>
<!-- End section "Order of Exclusions" -->
<div class="issue-marker wrapper">
<div class="issue-marker" data-bug_id="15183" data-bug_status="NEW">
<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=15183">Issue-15183</a>
<div class="issue-details">
<p class="short-desc">Is the CSS exclusions processing model incorrect?</p>
</div>
</div>
</div>
<div class="issue">
<p>The current draft provides a model for exclusions
without a collision-avoidance model.
The existing exclusion model in CSS uses floats,
which have both exclusion and collision-avoidance behavior.
Concerns have been raised that allowing exclusions
without collision avoidance could be harmful,
particularly with absolutely-positioned elements.
Three options should be considered:<p>
<ol>
<li>Allow exclusions in positioning schemes
with no collision avoidance.</li>
<li>Disallow exclusions in positioning schemes
with no collision avoidance.</li>
<li>Define collision-avoidance behavior
for positioning schemes without it,
and use this behavior by default with exclusions.</li>
</ol>
</div>
<h3 id="exclusions-processing-model">Processing model</h3>
<h4 id="exclusions-processing-model-description">Description</h4>
<p>Applying exclusions is a two-step process:</p>
<ul>
<li><strong>Step 1</strong>: resolve exclusion boxes belonging to each <span>wrapping context</span></li>
<li><strong>Step 2</strong>: resolve <span>wrapping context</span>s and lay out each containing block in turn:
<ul>
<li><strong>Step 2-A</strong>: resolve the position and size of exclusion boxes</li>
<li><strong>Step 2-B</strong>: lay out containing block, wrapping around <span>exclusion areas</span></li>
</ul>
</li>
</ul>
<h4 id="step-1-resolve-exclusion-boxes-belonging-to-each-wrapping-context">Step 1: resolve exclusion boxes belonging to each <span>wrapping context</span></h4>
<p>In this step, the user agent determines which <a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">containing block</a> each
<span>exclusion area</span> belongs to. This is a simple step, based on the
definition of containing blocks and elements with a computed value for 'wrap-flow'
that is not <code class="css">auto</code>.</p>
<h4 id="step-2-resolve-wrapping-contexts-layout-containing-blocks">Step 2: resolve wrapping contexts and lay out containing blocks</h4>
<p>In this step, starting from the
top of the <a href="https://www.w3.org/TR/CSS2/visuren.html#z-index">rendering tree</a> (see [[!CSS21]]),
the the agent processes each containing block in two sub-steps.</p>
<h4 id="step-2-A-resolve-exclusions-position-and-size">Step 2-A: resolve the position and size of exclusion boxes</h4>
<p>Resolving the position and size
of <span>exclusion boxes</span>
in the <span>wrapping context</span>
may or may not require a layout.
For example,
if an <span>exclusion box</span>
is absolutely positioned and sized,
a layout may not be needed
to resolve its position and size.
In other situations,
laying out the containing block's content is required.</p>
<p>When a layout is required,
it is carried out
without applying any <span>exclusion area</span>.
In other words,
the containing block is laid out
without a <span>wrapping context</span>. </p>
<p>Step 2-A yields a position and size
for all <span>exclusion boxes</span>
in the <span>wrapping context</span>.
Each exclusion box is processed in turn,
starting from the top-most,
and each <span>exclusion area</span>
is computed and contributed
to the <a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">containing block's</a>
<span>wrapping context</span>. </p>
<p>Scrolling is ignored in this step
when resolving the position and size
of 'position:fixed' <span>exclusion boxes</span>.</p>
<p>Once the <a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">containing block's</a>
<span>wrapping context</span> is computed,
all <span>exclusion boxes</span>
in that <span>wrapping context</span>
are removed from the normal flow.</p>
<h4 id="step-2-B-layout-containing-block-applying-wrapping">Step 2-B: lay out containing block applying wrapping</h4>
<p>Finally, the content
of the containing block is laid out,
with the inline content wrapping around
the <span>wrapping content</span>'s
<span>exclusion areas</span>
(which may be different
from the <span>exclusion box</span>
because of the 'shape-outside' property).</p>
<p>When the containing block itself is an <span>exclusion box</span>, then
rules on <a href="#exclusions-order">exclusions order</a> define which exclusions
affect the inline and descendant content of the box.</p>
<h4 id="exclusions-processing-model-example">Example</h4>
<p>This section illustrates the exclusions processing model with an example. It is meant
to be simple. Yet, it contains enough complexity to address the issues of
layout dependencies and re-layout.</p>
<p>The code snippet in the following example has two exclusions affecting
the document's inline content.</p>
<div class="example">
<pre class="html"><html>
<style>
#d1 {
position:relative;
height: auto;
color: #46A4E9;
border: 1px solid gray;
}
#e1 {
wrap-flow: both;
position: absolute;
left: 50%;
top: 50%;
width: 40%;
height: 40%;
border: 1px solid red;
margin-left: -20%;
margin-top: -20%;
}
#d2 {
position: static;
width: 100%;
height: auto;
color: #808080;
}
#e2 {
wrap-flow: both;
position: absolute;
right: 5ex;
top: 1em;
width: 12ex;
height: 10em;
border: 1px solid lime;
}
</style>
<body>
<div id="d1">
Lorem ipsusm ...
<p id="e1"></p>
</div>
<div id="d2">
Lorem ipsusm ...
<p id="e2" ></p>
</div>
</body>
</html></pre>
</div>
<p>The following figures illustrate:</p>
<ul>
<li>the document's DOM tree</li>
<li>the layout tree of generated block boxes</p>
</ul>
<div class="figure">
<img src="images/processing-model-example-dom.svg" width="200"
alt="DOM tree nodes"/>
<p class="caption">DOM tree</p>
</div>
<div class="figure">
<img src="images/processing-model-example-layout-tree.svg" width="350"
alt="Layout tree boxes"/>
<p class="caption">Layout tree of generated block boxes</p>
</div>
<h5>Step 1: resolve exclusion boxes belonging to each <span>wrapping context</span></h5>
<p>The figures illustrate how the boxes corresponding to the element sometimes
have a different containment hierarchy in the layout tree than in the DOM tree.
For example, the box generated by <code class="idl">e1</code> is positioned in
its containing block's box, which is the <code class="idl">d1-box</code>, because
<code class="idl">e1</code> is absolutely positioned and <code class="idl">d1</code>
is relatively positioned. However, while <code class="idl">e2</code> is also absolutely
positioned, its containing block is the initial containing block (ICB). See the
section 10.1 of the CSS 2.1 specification ([[!CSS21]]) for details.</p>
<p>As a result of the computation of containing blocks for the tree, the boxes belonging
to the <span>wrapping context</span>s of all the elements can be determined:</p>
<ul>
<li>The <span>wrapping context</span> for the html element contains the <code class="idl">e2</code> box: WC-1 (Wrapping Context 1)</li>
<li>The <span>wrapping context</span> for the body element inherits the html element's <span>wrapping context</span>: WC-1</li>
<li>The <span>wrapping context</span> for <code class="idl">d1</code> inherits the body element's
<span>wrapping context</span> and adds the <code class="idl">e1-box</code> to it. So the wrapping
context is made of both the <code class="idl">e1-box</code> and the
<code class="idl">e2-box</code>: WC-2</li>
<li>The <span>wrapping context</span> for <code class="idl">d2</code> inherits the body element's
<span>wrapping context</span>: WC-1</li>
</ul>
<h5>Step 2: resolve wrapping contexts and lay out containing blocks</h5>
<p>In this step, each containing block is processed in turn. For each containing block,
we (conceptually) go through two phases:</p>
<ol>
<li>resolve the <span>wrapping context</span>: resolve the position and size of its exclusions</li>
<li>lay out the containing block</li>
</ol>
<p>In our example, this breaks down to:</p>
<ol>
<li>resolve the position and size of the exclusions belonging to WC-1: RWC-1 (Resolved Wrapping Context 1).</li>
<li>lay out the initial containing block (i.e., lay out its content):
<ol>
<li>resolve the html element's <span>wrapping context</span>: RWC-1</li>
<li>lay out the html element:
<ol>
<li>resolve the body element's <span>wrapping context</span>: RWC-1</li>
<li>lay out the body element:
<ol>
<li>resolve the <code class="idl">d1</code> element's <span>wrapping context</span>: RWC-2</li>
<li>lay out the <code class="idl">d1</code> element</li>
<li>resolve the <code class="idl">d2</code> element's <span>wrapping context</span>: RWC-1</li>
<li>lay out the <code class="idl">d2</code> element</li>
</ol>
</li>
</ol>
</li>
</ol>
</li>
</ol>
<h6>Resolving RWC-1</h6>
<p>The top-most <span>wrapping context</span> in the layout tree contains the <code class="idl">e2</code>
exclusion. Its position and size needs to be resolved. In general, computing an
exclusion's position and size may or may not require laying out other content.
In our example, no content needs to be laid out to resolve the <code class="idl">e2</code>
exclusion's position because it is absolutely positioned and its size can be resolved
without layout either. At this point, RWC-1 is resolved and can be used when
laying inline content out.</p>
<h6>Resolving RWC-2</h6>
<p>The process is similar: the position of the
<code class="idl">e1</code> exclusion needs to be resolved. Again, resolving the exclusion's
position and size may require processing the containing block (d1 here).
It is the case here because the size and position of
<code class="idl">e1</code> depend on resolving the percentage lengths. The percentages are relative
to the size of
<code class="idl">d1</code>'s box. As a result, in order to resolve