Mercurial > drafts / file revision

 <h1>CSS Page Floats</h1>

 <pre class='metadata'>

 TR: http://www.w3.org/TR/css-page-floats-3/

 Status Text: Some of the features in this draft were previously published in <cite>CSS Generated Content for Paged Media Module</cite> [[CSS3GCPM]].

 Shortname: css-page-floats

 Level: 3

 Group: csswg

 Status: ED

 Work Status: Exploring

 ED: https://drafts.csswg.org/css-page-floats/

 Previous Version: http://www.w3.org/TR/2015/WD-css-page-floats-3-20150915/

 Editor: Johannes Wilm, Vivliostyle, [email protected]

 Former Editor: Håkon Wium Lie, Opera Software, [email protected]

 Abstract: This document describes floats that move to the top or bottom of content

 Abstract: passages. This feature has traditionally been used in print

 Abstract: publications in which figures and photos are moved to the top or bottom

 Abstract: of columns or pages, along with their captions.

 Abstract: This draft describes how to achieve this effects for floats within pages,

 Abstract: columns, regions and elements.

 Ignored Terms: near, 3em, intrude, top-corner, bottom-corner, left, right, both, element, none, floats, inline, max-width, max-height

 </pre>

 <h2 id="overview">Overview</h2>

   <em>This section is not normative.</em>

   This specification adds new keywords on the 'float' property.

   This document allows to specify whether a <a>float</a> floats to align with a

   <a>float reference</a> inline box, column, region or page. In the case of floats

   with a reference <a>fragmentation container</a>, placement can be deferred to a

   subsequent <a>fragmentation container</a> with the <em>float-defer</em> properties.

   New values on the 'clear' property add further ways of refining layouts.

   The way contents wrap around floats can be controlled by changing the value of

   the 'wrap-flow' property which initially is set to 'both' for page floats.

   <p class="issue">

     Page floats as defined here work with different types of fragmentation types

     (columns, regions, pages) as well as container elements. The specification

     is no longer specific to print or to pages.

     At the same time, inline floats and page floats differ in many ways, and it may

     (or may not) be a good idea to separate the two entirely.

     Therefore, the name <em>CSS Page Floats</em> should probably be replaced with

     a more appropriate name.

   </div>

 <h2 id="terms">

 Terminology</h2>

   <dl export>

     <dt><dfn>Float</dfn>

     <dd>

       An element which has float set to something else than none.

     <dt><dfn>Inline float</dfn>

     <dd>

       A float which has float set to inline.

     <dt><dfn>Page float</dfn>

     <dd>

       A float which has float set to something else than inline or none.

     <dt><dfn>Float block formatting context</dfn>

     <dd>

       The block formatting context which is generated by a float and which contains

       its contents.

     <dt><dfn>Float anchor</dfn>

     <dd>

       The float anchor is the point in the flow where the float had appeared had

       it not been a float and instead had been an empty inline element with no

       margins, borders or padding.

     <dt><dfn>Float containing block formatting context</dfn>

     <dd>

       The block formatting context inside of which an float is embedded.

     <dt><dfn>Initial float reference</dfn>

       <dd>

         The entity to which the float is aligned initially, before float

         placement takes place.

     <dt><dfn>Float reference</dfn>

     <dd>

       The entity to which the float is aligned.

     <dt><dfn>Not overlapping</dfn>

     <dd>

       Two elements are not overlapping if the margin box of one element is not

       overlapping the margin box of the other element.

   </dl>

 <h2 id="floating">

 Floating to the inline-start/inline-end and block-start/block-end</h2>

   <p>

     Floating elements can float to the start or end of the <a>float anchor</a>'s line or

     block, specified by the 'float' attribute. The floats are aligning to the start

     or end of a <a>float reference</a>, specified by the 'float-reference' attribute. The

     <a>float reference</a> can be the <a>float anchor</a>'s line box, column, region or page.

   <h3 id="float-reference-property">The 'float-reference' property</h3>

   <pre class="propdef">

     Name: float-reference

     Value: inline | column | region | page

     Initial: inline

     Applies to: all elements.

     Inherited: no

     Percentages: N/A

     Media: visual

     Computed value: as specified.

     Animatable: no

   </pre>

   <dl dfn-for="float-reference" dfn-type="value">

     <dt><dfn>inline</dfn>

     <dd>

       The <a>float reference</a> is the line box of the <a>float anchor</a>.

       The <a>float containing block formatting context</a> is the same as that of the

       <a>float anchor</a>.

       The float is an <a>inline float</a>.

     <dt><dfn>column</dfn>

     <dd>

       The <a>float reference</a> is the column in a multi column environment in

       which the <a>float anchor</a> is placed. If the <a>float anchor</a> is not

       inside a column, the <a>float reference</a> is the line box of the <a>float

       anchor</a>.

       The <a>float containing block formatting context</a> is a new block formatting

       context with the same dimensions and placement as the <a>float reference</a>.

       The float is a <a>page float</a>.

     <dt><dfn>region</dfn>

     <dd>

       The <a>float reference</a> is the region in a region-chain within which the

       <a>float anchor</a> is placed. If the <a>float anchor</a> is not inside a

       region, the <a>float reference</a> is the line box of the <a>float

       anchor</a>.

       The <a>float containing block formatting context</a> is a new block formatting

       context with the same dimensions and placement as the <a>float reference</a>.

       The float is a <a>page float</a>.

     <dt><dfn>page</dfn>

     <dd>

       The <a>float reference</a> of the float is the page within which the <a>float

       anchor</a> is placed. If the <a>float anchor</a> is not inside a page, the

       <a>float reference</a> is the line box of the <a>float anchor</a>.

       The <a>float containing block formatting context</a> is a new block formatting

       context with the same dimensions and placement as the <a>float reference</a>.

       The float is a <a>page float</a>.

   </dl>

   <div class="issue">

     The <a>float containing block formatting context</a> having the same dimensions

     as the <a>float reference</a> means that all floats that are not inline floats

     cannot move outside of their float references. Is this wanted?

   </div>

   <div class="issue">

     It is not possible to specify a block element which element to use as the

     reference element. This has been requested.

     Maybe something like:

     <pre><code>

 <style>

 .float {

 float-reference: float-container;

 }

 #container {

 float-container: true;

 }

 </style>

 <div id="container">

 <p>First paragraph<span class="float">FLOAT</span></p>

 <p>Second paragraph

 <span class="inline-block">[<span class="float">FLOAT</span>] </span>

 And some more text</p>

 </div>

     </code></pre>

     This should float both floats with reference to the <div id="container">

     element, rather than the <P> and inline <SPAN> elements.

   </div>

 <h3 id="float-property">The 'float' property</h3>

 <pre class="propdef">

   Name: float

   Value: block-start | block-end | inline-start | inline-end | snap-block | snap-inline | left | right | top | bottom | none

   Initial: none

   Applies to: all elements.

   Inherited: no

   Percentages: N/A

   Media: visual

   Computed value: as specified.

   Animatable: no

 </pre>

 <dl dfn-for="float" dfn-type="value">

   <dt><dfn>inline-start</dfn>

   <dd>

     If the <a>float reference</a> is a line box, the element generates a box that

     is floated to the line-start outer edge of the <a>float reference</a> and

     content flows on the line-end side of the box.

     If the <a>float reference</a> is not a line box, the element generates a box

     that is floated to the line-start and block-start outer edges of the <a>float

     reference</a>.

   <dt><dfn>inline-end</dfn>

   <dd>

     If the <a>float reference</a> is a line box, the element generates a box that

     is floated to the line-ebd  outer edge of the <a>float reference</a> and

     content flows on the line-start side of the box.

     If the <a>float reference</a> is not a line box, the element generates a box

     that is floated to the line-end and block-end outer edges of the <a>float

     reference</a>.

   <dt><dfn>block-start</dfn>

   <dd>

     If the <a>float reference</a> is a line box, block-start behaves like

     inline-start.

     If the <a>float reference</a> is not a line box, the element generates a box

     that is floated to the block-start and line-start outer edges of the <a>float

     reference</a>.

     The initial value of the <a>max-width</a> or <a>max-height</a> property that

     refers to the <a>inline size</a> of the float is '100%'.

     Content flows on the block-end side of the box.

   <dt><dfn>block-end</dfn>

   <dd>

     If the <a>float reference</a> is a line box, block-end behaves like inline-end.

     If the <a>float reference</a> is not a line box, the element generates a box

     that is floated to the block-end and line-end outer edges of the <a>float

     reference</a>.

     The initial value of the <a>max-width</a> or <a>max-height</a> property that

     refers to the <a>inline size</a> of the float is '100%'.

     Content flows on the block-start side of the box.

   <dt><dfn>left</dfn>

   <dd>

     If the <a>float reference</a> is a line box, behaves like inline-start or

     inline-end, whichever corresponds to line-left for the float reference.

     Otherwise, behaves like block-end, inline-start or inline-end depending on

     the float containing block’s 'direction' and 'writing-mode'.

   <dt><dfn>right</dfn>

   <dd>

     If the <a>float reference</a> is a line box, behaves like inline-start or

     inline-end, whichever corresponds to line-right for the float reference.

     Otherwise, behaves like block-start, inline-start or inline-end depending on

     the float containing block’s 'direction' and 'writing-mode'.

   <dt><dfn>top</dfn>

   <dd>

     Behave like block-start or inline-start depending on the float

     containing block’s 'direction' and 'writing-mode'.

   <dt><dfn>bottom</dfn>

   <dd>

     Behave like block-end or inline-end depending on the float

     containing block’s 'direction' and 'writing-mode'.

   <dt><dfn>snap-block(&lt;length> [, start | end | near ]?)</dfn>

   <dd>

       Has no effect if the element is an <a>inline float</a>.

       If the element is a <a>page float</a>, it makes the element float to the

       start or the end of the block if it naturally appears within a certain

       distance from either one. The length value(s) specifies the maximum

       distance from the start/end that an element must be within in order to be

       floated; one length value specifies the distance from both the start and

       the end, two length values specify the distance from the start and end,

       respectively.

       The optional keyword value specifies where the element is floated: start,

       end, or the nearest of the two. The initial value is 'near'. If 'near'

       is in effect and the element is within the specified distance both from

       the start and the end, end wins.

   <dt><dfn>snap-block</dfn>

   <dd>same as <code>snap-block(2em, near)</code>

   <dt><dfn>snap-inline(&lt;length> [, left | right | near ]?)</dfn>

   <dd>

       Has no effect if the element is an <a>inline float</a>.

       If the element is a <a>page float</a>, it makes the element float to the

       line start or line end if it naturally appears within a certain distance

       from the start or end of the line. The length value(s) specifies the

       maximum distance from the start/end that an element must be within in

       order to be floated; one length value specifies the distance from both the

       start and the end, two length values specify the distance from the start

       and end, respectively.

       The optional keyword value specifies where the element is floated: line

       start, line end, or the nearest of the two. The initial value is 'near'.

       If 'near' is in effect and the element is within the specified distance

       both from the start and the end, end wins.

   <dt><dfn>snap-inline</dfn>

   <dd>same as <code>snap-inline(2em, near)</code>

   <dt><dfn>none</dfn>

   <dd>The box is not floated.

 </dl>

 <div class="issue">

   There is currently no way to float into a combination of directions (top right,

   right top, left bottom, bottom left, etc.).

 </div>

 <div class="example">

   Float figure to top of reference column:

 <pre>

 .figure { float-reference: column; float: top }

 </pre>

   <img alt="sample rendering" src="images/7.png">

 </div>

 <div class="example">

   In this example a block-start float that does not fill the entire <a>inline size</a>

   of the float reference is placed at the start of the block and line.

 <pre>

 .figure { float-reference: column; float: block-start; width: 50% }

 </pre>

   <img alt="sample rendering" src="images/block_line_start.png">

 </div>

 <div class="example">

   In this example, a figure naturally appears close to a column break. There is

   not enough space for the figure in the first column, and it is therefore placed

   in the second column, leaving white space at the bottom of the first column.

   <img alt="sample rendering" src="images/23.png">

   To avoid the white space, the image can be floated to the nearest edge (in the

   block direction):

 <pre>

 .figure { float-reference: column; float: snap-block }

 </pre>

   In this example, the figure is already at the nearest edge, so it does not

   move. However, floats allow subsequent content to be displayed before the

   float and the white space can therefore be filled:

   <img alt="sample rendering" src="images/7.png">

 </div>

 <div class="example">

   In this example, two figures naturally appear in the text flow:

   <img alt="sample rendering" src="images/20.png">

   A typographer would typically try to avoid single lines of text above/below

   figures, which can be achieved with:

 <pre>

 div.figure { float-reference: column; float: snap-block(1.5em) }

 </pre>

   The length value specifies the reach of the snap function; in this example the

   second figure is affected, but not the first.

 </div>

 <div class="example">

   In this example, two figures naturally appear in the text flow:

   <img alt="sample rendering" src="images/20.png">

   To make the figures snap to the nearest edges, this code can be applied:

 <pre>

 div.figure { float-reference: column; float: snap-block(2.5em) }

 </pre>

   The resultant rendering is:

   <img alt="sample rendering" src="images/22.png">

 </div>

 <div class="example">

   In this example, tables will snap to the top/bottom if the top/bottom of the

   border box is closer than '3em' from the top/bottom of the float-reference

   which is a block element.

 <pre>

 table { float: snap }

 table { float: snap-block(3em) }

 table { float: snap-block(3em, bottom) }

 table { float: snap-block(3em 2em, bottom) }

 </pre>

 </div>

   <div class="note">

     More examples with regions as <a>float reference</a>s needed.

   </div>

 <h2 id="clearing_page_floats">

 The 'clear' property</h2>

   <pre class="propdef">

     Name: clear

     Value: inline-start | inline-end | block-start | block-end | left | right | top | bottom | none

     Initial: none

     Applies to: block-level elements, floats, regions, pages

     Inherited: no

     Percentages: N/A

     Media: visual

     Computed value: as specified.

     Animatable: no

   </pre>

   To prevent stacking of floats, the 'clear' property can be used:

   <dl dfn-for="clear" dfn-type="value">

     <dt><dfn>inline-start</dfn>

     <dd>

       If applied to an inline float, requires that the block-start outer edge of

       the box comes after the block-end outer edge of any inline-start-floats

       with an inline-start-float-reference that resulted from elements earlier

       in the source document.

       If applied to a <a>page float</a>, the <a>float reference</a> in which the

       page float is placed will be seen as full when determining whether it can

       host subsequent page floats that float in the inline-start direction.

     <dt><dfn>inline-end</dfn>

     <dd>

       If applied to a block-level element or an <a>inline float</a>, requires

       that the block-start outer edge of the box comes after the block-end outer

       edge of any inline-end-floats with an inline-end-float-reference that

       resulted from elements earlier in the source document.

       If applied to a <a>page float</a>, the <a>float reference</a> in which the

       page float is placed will be seen as full when determining whether it can

       host subsequent page floats that float in the inline-end direction.

     <dt><dfn>block-start</dfn>

     <dd>

       If applied to a block-level element or an <a>inline float</a>, behaves like

       inline-start.

       If applied to a page float, the <a>float reference</a> in which the page

       float is placed will be seen as full when determining whether it can host

       subsequent page floats that float in the block-start direction.

     <dt><dfn>block-end</dfn>

     <dd>

       If applied to a block-level element or an <a>inline float</a>, behaves

       like inline-end.

       If applied to a page float, the <a>float reference</a> in which the page float

       is placed will be seen as full when determining whether it can host

       subsequent page floats that float in the block-end direction.

     <dt><dfn>left</dfn>

     <dd>

       Behave like block-end, inline-start or inline-end depending on the float

       containing block’s 'direction' and 'writing-mode'.

     <dt><dfn>right</dfn>

     <dd>

       Behave like block-start, inline-start or inline-end depending on the float

       containing block’s 'direction' and 'writing-mode'.

     <dt><dfn>top</dfn>

     <dd>

       Behave like block-start or inline-start depending on the float

       containing block’s 'direction' and 'writing-mode'.

     <dt><dfn>bottom</dfn>

     <dd>

       Behave like block-end or inline-end depending on the float

       containing block’s 'direction' and 'writing-mode'.

     <dt><dfn>both-inline</dfn>

     <dd>

       Behave like inline-start and inline-end.

     <dt><dfn>both-block</dfn>

     <dd>

       Behave like block-start and block-end.

     <dt><dfn>both</dfn>

     <dd>

       Behave like both-inline.

     <dt><dfn>all</dfn>

     <dd>

       Behave like both-block and both-inline.

   </dl>

   <div class="example">

     In this example, the two figures may appear in the same column:

 <pre>

 .figure { float-reference: column; float: bottom; clear: none }

 &ltdiv class=figure></div>

 &ltdiv class=figure></div>

 </pre>

     <img alt="sample rendering" src="images/16.png">

   </div>

   <div class="example">

     In this example, the two figures will appear in different columns:

 <pre>

 .figure { float-reference: column; float: bottom; clear: bottom }

 &ltdiv class=figure></div>

 &ltdiv class=figure></div>

 </pre>

     <img alt="sample rendering" src="images/17.png">

   </div>

   <div class="example">

     In this example, the two figures may appear at the bottom of the same column

     due to clearing only at the top:

 <pre>

 .figure { float-reference: column; float: bottom; clear: top }

 &ltdiv class=figure></div>

 &ltdiv class=figure></div>

 </pre>

     <img alt="sample rendering" src="images/16.png">

   </div>

   <div class="example">

     In this example, the two figures will appear in different columns due to

     clearing at the bottom:

 <pre>

 .figure { float-reference: column; float: bottom; clear: bottom }

 &ltdiv class=figure></div>

 &ltdiv class=figure></div>

 </pre>

     <img alt="sample rendering" src="images/17.png">

   </div>

   <div class="example">

     In this example, the two figures end up the top corner of two different

     pages:

 <pre>

 .figure { float-reference: page; float: top; clear: top }

 &ltdiv class=figure></div>

 &ltdiv class=figure></div>

 </pre>

   </div>

   <div class="example">

     In this example, the two figures request different positions, and they may

     therefore end up in the same column:

 <pre>

 .figure.one { float-reference: column; float: top; clear: top }

 .figure.two { float-reference: column; float: bottom; clear: bottom }

 &ltdiv class="figure one"></div>

 &ltdiv class="figure two"></div>

 </pre>

   </div>

 <h2 id="deferring_floats">Deferring page floats</h2>

   Users can influence the placement of a <a>page float</a> by deferring them to

   another <a>fragmentation container</a> than where the <a>float anchor</a> is

   placed.

   A float that is an <a>inline float</a> cannot be deferred.

   Float deferring assigns an <a>initial float reference</a>, yet float stacking

   can lead page floats being moved to a subsequent <a>fragmentation container</a>

   if their <a>initial float reference</a> lacks the space to host them.

   The 'float-defer' property is introduced to control deferring floats:

   <h3 id="float-defer-property">The 'float-defer' property</h3>

     <pre class="propdef">

       Name: float-defer

       Value: &ltinteger> | last | none

       Initial: none

       Applies to: floats

       Inherited: no

       Percentages: N/A

       Media: visual

       Computed value: as specified.

       Animatable: no

     </pre>

     This property specifies whether the <a>initial float reference</a> of a <a>page

     float</a> is the <a>fragmentation container</a> in which the <a>float anchor</a>

     is placed after previous page floats have been placed, or in another one.

     This property is ignored if the element is an <a>inline float</a>.

     Values are:

     <dl>

       <dt>none

       <dd>The <a>initial float reference</a> is the <a>fragmentation container</a> in which the

       <a>float anchor</a> is placed after all previous page floats have been placed.

       <dt>&lt;integer>

       <dd>

         A positive integer value indicates that the <a>initial float reference</a> of

         the page float should be Nth <a>fragmentation container</a> of the `fragmentation

         flow`, where N is the value of the `float-defer` property plus the order

         number of the <a>fragmentation container</a> in which the <a>float anchor</a> is placed

         after all previous page floats have been placed within the given

         <a>fragmentation context</a>. If N is larger than the order number of the last

         <a>fragmentation container</a> within the given <a>fragmentation context</a> at the time of

         assignment, then N is the order number of the last <a>fragmentation container</a>

         within the given <a>fragmentation context</a>.

         A negative integer value indicates that the <a>initial float reference</a> of

         the page float should be a <a>fragmentation container</a> of the

         <a>fragmentation context</a>, counting backward from the end, so that -1

         is the last <a>fragmentation container</a>, -2 is the next-to-last, etc. .

         In the case of a negative integer value, the <a>initial float reference</a> is the

         Nth <a>fragmentation container</a> of the <a>fragmentation context</a>, where N is 1

         plus the order number of the last <a>fragmentation container</a> within the given

         <a>fragmentation context</a> after all previous page floats have been placed plus

         the value of the `float-defer` property.

         Zero is the same as `none`.

         If the value of the `float-defer` property would cause the <a>initial float

         reference</a> to be an inexistent <a>fragmentation container</a>, the property

         is interpreted as if it were zero.

         <p class="note">

           Negative float-defer values put the initial float reference a certain number

           to be a certain amount of fragmentation containers from the last fragmentation

           container at the time of of the placement. Subsequent page float stacking

           can mean that a page float is being placed in a later fragmentation container

           (a page float with float-defer set to -3 can end up being placed in the

           last fragmentation container), and later page floats may mean that new

           fragmentation containers are added, so that the a fragmentation container

           that previously was Nth last fragmentation container within a fragmentation

           context now is the N+Xth last. Additional fragmentation container(s) that

           are added after the page float was placed, will not cause the page float

           to be moved.

       <dt>last

       <dd>

         The <a>initial float reference</a> is the last <a>fragmentation container</a> within

         the given <a>fragmentation context</a> after all previous page floats have been

         placed.

     </dl>

     <div class="example">

       Float figure to the top of the region that follows the region in which

       the <a>float anchor</a> is placed:

 <pre>

 .figure { float-reference: region }

 .figure { float: top }

 .figure { float-defer: 1 }

 </pre>

     </div>

     <div class="example">

       Float figure to the top of the next-to-last column:

 <pre>

 .figure { float-reference: column; float: top; float-defer: -2 }

 </pre>

       <img alt="sample rendering" src="images/7.png">

     </div>

     <div class="example">

       Float figure to the top of the last page:

 <pre>

 .figure { float-reference: page }

 .figure { float: top }

 .figure { float-defer: -1 }

 </pre>

     </div>

     <div class="example">

       Float figure to the top of the last column:

 <pre>

 .figure { float-reference: column }

 .figure { float: top }

 .figure { float-defer: last }

 </pre>

     </div>

     <div class="example">

       Float figure to top of the last column:

 <pre>

 .figure { float-reference: column; float: top; float-defer: last }

 </pre>

 <img alt="sample rendering" src="images/6.png">

     </div>

 <h2 id="wrapping-around-page-floats">Wrapping around page floats</h2>

   Page floats have their 'wrap-flow' property set to 'both' initially and are

   treated like exclusions. This specification does not make any further

   specification about wrapping contents around page floats.

   <div class="issue">

     Should the 'wrap-flow' really be set to both, or should the flow be restricted

     to only be on one side?

   </div>

 <h2 id="the-float_offset-property">The 'float-offset' property</h2>

   <pre class="propdef">

     Name: float-offset

     Value: <length> | <percentage>

     Initial: 0

     Applies to: floats

     Inherited: no

     Percentages: see prose

     Media: visual

     Computed value: one absolute length

     Animatable: no

   </pre>

   This property pushes a <a>page float</a> in direction opposite of the where it has been

   floated with 'float'.

   If the element is an <a>inline float</a>, this property is ignored.

   This property can only influence a <a>page float</a> along an axis along which

   it has been floated.

   <dl>

     <dt>&lt;percentage></dt>

     <dd>

       Percentage values are computed according to this formula:

     <pre>

       (containing-block-width - float-width) * percentage

       (containing-block-height - float-height) * percentage

     </pre>

     </dd>

   </dl>

   <div class="example">

 <pre>

 img {

   float-reference: column;

   float: left;

   float-offset: 2em;

 }

 </pre>

     In this example, the image is floated to the left. Therefore, 'float-offset'

     may only push the element to the right.

   </div>

   <div class="example">

 <pre>

 img {

   float-reference: column;

   float: right;

   float-offset: 5px;

 }

 </pre>

     <img alt="sample rendering" src="images/14.png">

   </div>

   <!--div class="example">

     Pull quotes are often centered in a column. In this example, the pull quote is

     floated to the right, and then pushed back into the center.

     <img alt="sample rendering" src="images/region_pullquote.png">

 <pre>

 .pullquote {

   float-reference: region;

   float: right;

   float-offset: 50%; /* 50% centers the box */

 }

 </pre>

   </div-->

 <h2 id="page-float-placement">Page float placement</h2>

   The order of page floats placement is determined by the following rules:

   <ol>

     <li>

       All page floats with 'float-reference' set to `page` are placed, in

       document order, before those with 'float-reference' set to `region` and

       `column`.

     <li>

       Thereafter, page floats with 'float-reference' set to `column` and `region`

       are placed in document order.

     </li>

   </ol>

   The placement of a single page float is a process that has to be terminated

   entirely before the placement of a subsequent page float can be initiated. The

   placement process consists of the following steps:

   <ol>

     <li>Determine the <a>initial float reference</a> by considering the

     <a>fragmentation container</a> in which the <a>float anchor</a> is placed and

     the `float-defer` property of the page float. The <a>float reference</a> is

     initially set to be the same as the <a>initial float reference</a>.</li>

     <li>Determine if the given <a>float reference</a> has enough space or can be

     expanded to host the page float, if the rules of <a href="#float-stacking">

     float stacking</a> and <a href="#float-reference-growth">float reference

     growth</a> are to be followed. If this is not the case, and the <a>float

     reference</a> is not the last <a>fragmentation container</a> within the given

     <a>fragmentation context</a>, then make the following <a>fragmentation

     container</a> within the given <a>fragmentation context</a> the <a>float

     reference</a>. Repeat this step until the <a>float reference</a> can be

     expanded enough to host the page float or it is the last <a>fragmentation

     container</a> within the given <a>fragmentation context</a>.</li>

     <li>If the <a>float reference</a> is the last <a>fragmentation container</a> within

     the given <a>fragmentation context</a>, and it has not enough space and cannot be

     expanded to host the page float, then do the following:</li>

     <ol>

       <li>If the <a>fragmentation context</a> allows for the addition of another

       <a>fragmentation container</a> and an additional <a>fragmentation container</a>

       would have the needed size to host the page float, a new <a>fragmentation

       container</a> is added to the end of the <a>fragmentation context</a>. The

       <a>float reference</a> is set the newly created <a>fragmentation

       container</a>.</li>

       <li>Otherwise, if the <a>fragmentation container</a> is a region, then the

       'regionOverset` attribute of the <a>fragmentation container</a> is set to

       `overset`.

     </ol>

     <li>The page float is placed in the <a>float reference</a> according to the rules

     of 'float stacking' and 'float reference growth'.</li>

   </ol>

 <h3 id="float-reference-growth">Float reference growth</h3>

 Float references can grow up to the their `max-height` and `max-width` or their

 `available size`, whichever is the lowest, in order to accommodate page floats.

 <h3 id="float-stacking">Rules for page float stacking</h3>

 Page floats are stacked within a given <a>float reference</a> in the order of their

 placement and in the direction of the inline- and flow-directions of the

 <a>fragmentation context</a> while <a>not overlapping</a> with any other page

 floats with the same <a>float reference</a> and by keeping a distance N between

 the page float's margin edge and the padding edge of the <a>float reference</a>

 as well as between the page float's margin edge and the margin edge of the last

 previously placed page float with the same <a>float reference</a> and the same

 'float' value, where N is the 'float-offset' value of the page float.

 For the purpose of calculating whether enough space is available for a page floats

 within the <a>float reference</a>, it is assumed that the page floats in the block

 directions fill the entire line size of the <a>float reference</a> and page floats

 in the inline direction fill the entire block size of the <a>float reference</a>.

 For the purpose of placement, page floats in the block-start direction are also

 placed at the inline-start edge of the float reference and vice versa, and page

 floats in the block-end direction are placed at the inline-end edge of the float

 reference and vice versa.

 If the page float has a defined 'clear'-value, then the <a>float reference</a> in

 which the page float is placed is closed for all subsequent page floats that

 floating in the direction specified by the 'clear'-value.

 <p class="issue">

   We can effectively currently float to two corners: inline-start/block-start and

   inline-end/block-end. We should augment this with the option to have a secondary

   float direction to allow basic 2D floating.

 <h2 id="relation_to_absolutely_positioned_exclusions">

 Floats and absolutely positioned exclusions</h2>

 Floats and absolutely positioned exclusions share some common traits, but in the

 case of inline floats they are not the same. Floats that are not inline floats

 should behave the same as absolutely positioned exclusions with positions and

 sizes manually set to prevent overlap between floats and to prevent floats from

 moving beyond the edges of the float reference, with the float reference being

 grown as much as needed up to its maximum extend to accommodate all containing

 floats.

 <h3 id="inline_floats_and_absolutely_positioned_exclusions">

 Differences between inline floats and absolutely positioned elements</h3>

   <em>This section is not normative.</em>

   <p>

     Inline floats and absolutely positioned elements are both out-of-flow elements.

     Absolutely positioned elements that are also exclusions can imitate many of

     the features of floats.

   <p>

     However, in the case of inline floats, the block formatting context that

     contains them (the <a>float containing block formatting context</a>) is

     required to include the area occupied by the float, which is not a requirement

     for absolutely positioned elements.

   <div class="example">

     An inline float inside a <a>float containing block formatting context</a> given

     by a display-inline-block element. The element, which has a green border, is

     expanded to include the brown float.

 <pre><code>

 <style>

 .float {

   float: left;

   margin: 5px;

 }

 .border {

     border: 3px solid black;

     margin: 5px;

 }

 #outer {

     border: 1px solid green;

     display: inline-block;

 }

 canvas {

     background-color: brown;

 }

 p {

   margin: 5px;

 }

 </style>

 <div id="outer">

     <p class="border">

         <span class="float border">

             <canvas width="100" height="100"/>

         </span>

         First paragraph.

     </p>

     <p class="border">

         Second paragraph and some more text.

     </p>

 </div>

 </code></pre>

     <img alt="sample rendering" src="images/float_containing_context.png">

     In comparison, the below is the same HTML, but the float is replaced by an

     absolutely positioned element that is also an exclusion. The <a>float

     containing block formatting context</a> is still given by a

     display-inline-block element. However, the element, marked by a green border,

     does not expand to include the brown, absolutely positioned element.

 <pre><code>

 <style>

 .float {

     position: absolute;

     top: 8px;

     left: 8px;

     wrap-flow: both;

 }

 .border {

     border: 3px solid black;

     margin: 5px;

 }

 #outer {

     border: 1px solid green;

     display: inline-block;

     position: relative;

 }

 canvas {

     background-color: brown;

 }

 </style>

 <div id="outer">

     <p class="border">

         <span class="float border">

             <canvas width="100" height="100"/>

         </span>

         First paragraph.

     </p>

     <p class="border">

         Second paragraph and some more text.

     </p>

 </div>

 </code></pre>

     <img alt="sample rendering" src="images/positioned_containing_context.png">

   </div>

 <h2 id="overconstrained-page-floats">Overconstrained floats</h2>

   In many cases, the specified values on these properties cannot be honored.

   <div class="example">

     The number of columns is limited, and high values therefore cannot be honored:

 <pre>

 .figure { float-reference: column; float: top; float-defer: 1000 }

 </pre>

   </div>

   <div class="example">

     A narrow screen may only have room for one column, in which case this request

     cannot be honored:

 <pre>

 .figure { float-reference: column; float: top; float-defer: -5 }

 </pre>

   </div>

   <div class="example">

     In long documents, all content cannot fit on the last page, and this rule

     therefore cannot be honored:

 <pre>

 p { float-reference: page; float: top; float-defer: last }

 </pre>

   </div>

   Floats are processed in the order they appear in the source. However, the

   visual order of floats may not be the same as the source order.

   <div class="example">

     Consider this code:

 <pre>

 .one { float-reference: page; float: top; float-defer: last }

 .two { float-reference: column; float: top; clear: column }

 <div class=one></div>

 <div class=two></div>

 </pre>

     In this example, the first element requests to appear on the last page, while

     the second element requests to appear in the natural column. If the natural

     column of the second element appears on a page before the last page, the second

     element will appear visually before the first.

   </div>

   <div class="example">

     Consider this code:

 <pre>

 .one { float-reference: page; float: top; float-defer: last }

 .two { float-reference: page; float: top; clear: page; }

 <div class=one></div>

 <div class=two></div>

 </pre>

     If all content can fit on one page, the first page will also be the last page.

     The first element is processed first and is placed on top of the first page.

     Then the second element is processed. It requests a clear top, something which is

     not possible on the first page. Therefore, a second page is created and the

     first element is moved there. Even if the first element requests to be on the

     last page, it will not appear there.

   </div>

   When resolving over-constrained layouts, the order of importance for defined

   goals are:

   <ol>

     <li>honor 'clear: top/bottom'

     <li>honor 'float-defer'

     <li>honor 'float: top/bottom'

     <li>display all content (as described by other CSS properties)

     <li>keep the number of pages to a minimum

   </ol>

 <h2 class="no-num" id="acks">

 Acknowledgments</h2>

   This specification is made possible by input from

   Rossen Atanassov,

   Tab Atkins Jr.,

   David Baron,

   Lars Erik Bolstad,

   Bert Bos,

   Mike Bremford,

   Dave Cramer,

   Michael Day,

   Werner Donné,

   Brady Duga,

   James Elmore,

   Elika Etemad,

   Michel Fortin,

   Daniel Glazman,

   Melinda Grant,

   Ian Hickson,

   Laurens Holst,

   Brad Kemper,

   Toru Kawakubo,

   Rune Lillesveen,

   Peter Linss,

   Cameron McCormack,

   Paul E. Merrell,

   Del Merritt,

   Markus Mielke,

   Kelly Miller,

   Alex Mogilevsky,

   Peter Moulder,

   Shinyu Murakami,

   Michel Onoff,

   Anton Prowse,

   Liam R E Quin,

   Jacob Grundtvig Refstrup,

   Florian Rivoal,

   Christian Roth,

   Allan Sandfeld Jensen,

   Simon Sapin,

   Alan Stearns,

   Morten Stenshorne,

   Philip Taylor,

   Ian Tindale,

   Ladd Van Tol,

   Lea Verou,

   Tarquin (Mark) Wilton-Jones,

   Steve Zilles,

   Tantek Çelik

   and the CSS Working Group members.