CSS Regions Module Level 3

Abstract

The CSS regions module allows content to flow across multiple areas called regions. The regions are not necessarily contiguous in the document order. The CSS regions module provides an advanced content flow mechanism, which can be combined with positioning schemes as defined by other CSS modules such as the Multi-Column Module [CSS3COL] or the Grid Layout Module [CSS3-GRID-LAYOUT] to position the regions where content flows.

Status of this document

Note This document uses an experimental style sheet. We welcome your feedback on the styles at site-comments@w3.org.

This is a public copy of the editors' draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don't cite this document other than as work in progress.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “css3-regions” in the subject, preferably like this: “[css3-regions] …summary of comment…”

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This draft is related to the drafts about Multi-column Layout [CSS3COL], Grid Layout [CSS3GRID], Flexible Box Layout [CSS3-FLEXBOX], and Template Layout [CSS3LAYOUT].

Table of contents

• 1. Introduction
  • 1.1. Named flows and regions
  • 1.2. Regions styling
• 2. CSS regions concepts
  • 2.1. Regions
  • 2.2. Named flow
  • 2.3. Regions flow breaking rules
• 3. Relation to document events
• 4. Properties and rules
  • 4.1. The ‘flow-into’ property
  • 4.2. The ‘flow-from’ property
    • 4.2.1. Auto width on regions
    • 4.2.2. Auto height on regions
  • 4.3. Region flow break properties: ‘break-before’, ‘break-after’, ‘break-inside’
  • 4.4. The region-overflow property
  • 4.5. The @region rule
• 5. Pseudo-elements
  • 5.1. Processing model
• 6. CSSOM view and CSS regions
  • 6.1. The NamedFlow interface
  • 6.2. Extension to the Element interface
  • 6.3. Region flow layout events
• 7. Relation to other specifications
• 8. Use Cases
• 9. Conformance
• 10. Changes
  • 10.1. Changes from November 29^th 2011 version
  • 10.2. Changes from June 09^th 2011 version
• Acknowledgments
• References
  • Normative references
  • Other references
• Index
• Property index
• 11. Issue manager

1. Introduction

This section is non-normative.

Capturing the complex layouts of a typical magazine, newspaper, or textbook requires capabilities beyond those available in existing CSS modules. This is the purpose of the CSS regions module.

The CSS regions module can be seen as an extension of the concept of multi-column elements. With CSS Multi-column layout [CSS3COL], columns share the same dimensions and define column boxes organized in rows. Content flows from one column to the next.

The multi-column model is an example of flowing content from one area to another, where the areas are the multi-column element's column boxes and the flow is made of the multi-column element's children.

However, for more complex layouts, content needs to flow from one area of the page to the next without limitation of the areas' sizes and positions. These arbitrary areas are the target of specific content flows. In this document these areas are called regions, and the content flows are called named flows. Regions are based on the rectangular geometry of the CSS box model. Elements in a named flow are taken out of the normal visual formatting and rendered in a chain of regions.

1.1. Named flows and regions

Consider the layout illustrated in figure 1.

Layout requiring sophisticated content flow

The designer's intent is to position an image in region ‘A’ and to flow an article's text from region ‘1’, to region ‘2’, ‘3’ and ‘4’.

The following code snippet shows the content to flow between the regions 1, 2, 3 and 4.

<div id="article">
  <h1>Introduction</h1>
  <p>This is an example ...</p>
    
  <h1>More Details</h1>
  <p>This illustrates ...</p>
  <p>Then, the example ...</p>
  <p>Finally, this ...</p>
</div>
        

And the following snippet shows an example using grid cells to define the region areas:

<style>
    #page {
      width: 800px;
      height: 600px;
      grid-template: "aaa.e"
                     "....e"
                     "bbb.e"
                     "....e"
                     "c.d.e";
      grid-rows: 52% 4% 20% 4% 20%;
      grid-columns: 30% 5% 30% 5% 30%;
    }
    #regionA { grid-cell: a; }
    #region1 { grid-cell: b; }
    #region2 { grid-cell: c; }
    #region3 { grid-cell: d; }
    #region4 { grid-cell: e; }
</style>

<div id="page">
    <div id="region1"></div>        
    <div id="region2"></div>        
    <div id="region3"></div>        
    <div id="region4"></div>
</div>
    

Any of the CSS layout facilities can be used to create, position and size regions as needed.

However, there is no existing mechanism to associate the content with the regions so that content flows as intended. Figure 2 shows an example of the intended visual rendering of the content.

Sample rendering for desired layout

The CSS regions module is independent of the layout of regions and the mechanism used to create them. For simplicity, our example uses elements as regions as shown in the previous code snippet.

The following code example illustrates how the content of the article element becomes a flow and how the areas ‘region1’, ‘region2’, ‘region3’ and ‘region4’ become regions that consume the ‘article_flow’ content.

<style>

#article {
    flow-into: article_flow;
}

#region1, #region2, #region3, #region4 {
    flow-from: article_flow;
}
</style>

The ‘article_flow’ value on the ‘flow-into’ property directs the ‘#article’ element to the ‘article_flow’ named flow. Setting the elements' ‘flow-from’ property to ‘article_flow’ on elements makes them regions and associates these regions with the named flow: the flow is ‘poured’ into the desired regions.

1.2. Regions styling

Region styling allows content to be styled depending on the region it flows into. It is a form of context-based styling, similar to Media Queries [MEDIAQ] which enable or disable selectors depending on the rendering context. With region styling, additional selectors may apply depending on the region into which content flows.

In our example, the designer wants to make text flowing into region 1 larger, bold and dark blue. In addition, <h1> headers should be crimson.

This design can be expressed with region styling as shown below.

<style>
/*
 * Default article styling.
 */
#article {
    color:#777;
    text-align: justify;
}

#article h1 {
    border-left: 1px solid #777;
    padding-left: 2ex;
    display: run-in;
}

/*
 * Additional styling to apply to content when it falls into 
 * region1
 */
@region #region1 {
    #article {
        font-weight: bold;
        color: #0C3D5F;
        font-size: larger;
    }

    #article h1 {
        color: crimson;
        border: none;
        padding: 0px;
    }
}


/*
 * Style that would apply to region1's normal content but
 * will not apply to its named flow content.
 */
#region1 p {
    color: red;
}

</style>

The ‘@region’ rule for region 1 limits its selectors to content flowing into region 1. The following figure shows how the rendering changes if we do not increase the font size nor make it bold for content flowing into region 1. As more content can be fitted, more content is subject to the contextual selectors, resulting in more dark blue text into region 1.

Different rendering with a different region styling

Finally, note how the ‘red’ color specified for <p> elements under #region1 does not apply to content that flows into the region. This specified style does not apply to the named flow content because the <p> elements in the ‘article’ named flow are not descendants of the #region1 element and, consequently, the "#region1 p" selector does not apply to these elements.

2. CSS regions concepts

2.1. Regions

A region is an element that generates a block container box and has an associated named flow (see the ‘flow-from’ property).

2.2. Named flow

A named flow is the ordered sequence of elements associated with a flow with a given identifier. Elements in a named flow are ordered according to the document order.

Elements are placed into a named flow with the ‘flow-into’ property. The elements in a named flow are laid out in the chain of regions that are associated with this named flow. Regions are organized in to a region chain according to the document order.

Content from a named flow is broken up between regions according to the regions flow breaking rules.

2.3. Regions flow breaking rules

Breaking a named flow across multiple regions is similar to breaking a document's content across multiple pages (see [CSS3PAGE]) or a multi-column element's content across column boxes (see [CSS3COL]). One difference is that page boxes are generated based on the available content whereas regions are a set of recipient boxes for the named flow content whose dynamic generation is not in the scope of this specification.

Regions are organized in to a region chain.

Each region in turn consumes content from its associated named flow. The named flow content is positioned in the current region until a natural or forced region break occurs, at which point the current region becomes the next one in the region chain. If there are no more regions in the region chain and there is still content in the flow, the positioning of the remaining content is controlled by the ‘region-overflow’ property on the last region in the chain.

3. Relation to document events

The CSS regions module does not alter the normal processing of events in the document tree. In particular, if an event occurs on an element that is part of a named flow, the event's bubble and capture phases happen following the document tree order.

4. Properties and rules

This section is normative.

4.1. The ‘flow-into’ property

The ‘flow-into’ property can place an element into a named flow. Elements that belong to the same flow are laid out in the regions associated with that flow.

none

The element is not moved to a named flow and normal CSS processing takes place.

<ident>

The element is taken out of its parent's flow and placed into the flow with the name ‘<ident>’. The element is said to have a specified flow. The values ‘none’, ‘inherit’, ‘default’, ‘auto’ and ‘initial’ are invalid flow names.

A named flow needs to be associated with one or more regions for its elements to be visually formatted. If no region is associated with a given named flow, the elements in the named flow are not rendered: they do not generate boxes and are not displayed.

The children of an element with a specified flow may themselves have a specified flow.

If an element has the same specified flow as one of its ancestors, it becomes a sibling of it's ancestor for the purpose of layout in the regions laying out content from that flow.

The ‘flow-into’ property does not affect the CSS cascade and inheritance for the elements on which it is specified. The ‘flow-into’ property affects the visual formatting of elements placed into a named flow and of regions laying out content from a named flow.

The edges of the first region in a region chain associated with a named flow establish the rectangle that is the containing block used for absolutely positioned elements in the name named flow which do not have an ancestor with a ‘position’ of ‘absolute’, ‘relative’ or ‘fixed’ (see [CSS21]). That first region rectangle is used as the containing block instead of the initial containing block.

The first region defines the writing mode for the entire flow. The writing mode on subsequent regions is ignored.

Elements in a named flow are sequenced in document order.

table {flow-into: table-content}

table > * {flow-into: table-content} ...

table * {flow-into: table-content}

The ‘flow-into’ property does not apply to the ::first-line and ::first-letter pseudo-elements.

The effect of ‘flow-into’ on generated content such as ::marker, ::before and ::after is undefined. This may change depending on implementation feedback.

4.2. The ‘flow-from’ property

The ‘flow-from’ property makes an element a region and associates it with a named flow.

none

The element is not a region.

<ident>

If the ‘content’ property computes to something else than ‘normal’, the element does not become a region. If the ‘content’ property computes to ‘normal’, then the element becomes a region and is ordered in a region chain according to its document order. The content from the flow with the <ident> name will be broken into segments and visually formatted in the principal boxes of the regions in the region chain. If there is no flow with name <ident>, then the element does not format any content visually.
Likewise, if the element is part of the flow with name <ident>, then the element does not format any content visually.

Note A region's document children are not visually formatted unless they are directed to a named flow referenced by one or more regions.

<style>
  .article{
    flow-into: thread;
  }
  .region{
    flow-from: thread;
  }
</style>
<html>
  <body>
    <div class=region>div content</div>
  </body>
</html>
        

Regions create a new stacking context. Regions establish a new block formatting Context.

Floats or other exclusions (see [CSS3-EXCLUSIONS]) potentially impact the content laid out in regions, just as for non-regions.

4.2.1. Auto width on regions

A computed value of ‘auto’ for a region's ‘width’ property becomes a used value calculated based on the region's ::before and ::after generated content only.

4.2.2. Auto height on regions

A computed value of ‘auto’ for a region's ‘height’ property becomes a used value calculated based on the region's ::before and ::after generated content only.

4.3. Region flow break properties: ‘break-before’, ‘break-after’, ‘break-inside’

User agents laying out content in multiple regions must determine where content breaks occur. The problem of breaking content into segments fitting in regions is similar to breaking content into pages or columns.

Each break ends layout in the current region and causes remaining pieces of content from the named flow to be visually formatted in the following region in the region chain, if there is one.

The following extends the ‘break-before’, ‘break-after’ and ‘break-inside’ properties from the [CSS3COL] specification to account for regions. The additional values are described below.

These properties describe page, column and region break behavior before/after/inside the generated box. These values are normatively defined in [CSS3COL]:

This specification adds the following new values:

region

Always force a region break before (after) the generated box.

avoid-region

Avoid a region break before (after, inside) the generated box.

The behavior of region breaks with regards to regions is identical to the behavior of page breaks with regards to pages, as defined in the [CSS21].

4.4. The region-overflow property

The ‘region-overflow’ property controls the behavior of the last region associated with a named flow.

auto

Content flows as it would in a regular content element. If the content exceeds the container box, it is subject to the overflow property's computed value on the region element. Region breaks must be ignored on the last region.

break

If the content fits within the region element, then this property has no effect. If the content does not fit within the region element, the content breaks as if flow was going to continue in a subsequent region. See the breaking rules section. A forced region break takes precedence over a natural break point.

Flow content that follows the last break in the last region, if any is not rendered.

The ‘region-overflow’ property does not influence the size of the region it applies to.

The following code sample illustrates the usage of the ‘region-overflow’ property.

<style>
#article {
    flow-into: "article";
}

#region_1, #region_2 {
    flow-from: article;
    region-overflow: break; /* or none */
    overflow: visible; /* or hidden */
}

</style>

<div id="article">...</div>

<div id="region_1"></div>
<div id="region_2"></div>
        

‘flow-into: "article"’	region_1 and region_2	‘region-overflow: auto’ ‘overflow:visible’
	‘region-overflow: break’	‘region-overflow: auto’ ‘overflow:hidden’

Different values for the region-overflow property

4.5. The @region rule

An ‘@region’ rule contains style declarations specific to particular regions.

@region <selector> {
    ... CSS styling rules ...
}         
    

The ‘@region’ rule consists of the keyword ‘@region’ followed by a selector and a block of style rules. The ‘@region’ rule and the selector constitute the region's ‘flow segment’ selector. The region's flow segment selector specifies which range of elements in the flow are subject to the style rules in the following block: it applies to the range (see [DOM-LEVEL-2-TRAVERSAL-RANGE]) from the region's flow that flows in the selected region(s).

Elements that are fully or partially in the ‘flow segment’ may match any of the selectors found in the style rule. However, the style rules only apply to the portion of the element that falls into the corresponding region.

Only a limited list of properties can be set in a region style rule:

1. font properties
2. color property
3. background property
4. ‘word-spacing’
5. ‘letter-spacing’
6. ‘text-decoration’
7. ‘text-transform’
8. ‘line-height’
9. border properties
10. rounded corner properties
11. border images properties
12. margin properties
13. padding properties
14. ‘text-shadow’ property
15. ‘box-shadow’ property
16. ‘box-decoration-break’ property
17. ‘width’ property

In the following example, the named flow ‘article_flow’ flows through ‘region_1’ and ‘region_2’.

<style>
    #div_1 {
        flow-into: article_flow;
    }
    
    #region1, #region2 {
        flow-from: article_flow;
    }

    /* region style "RSA" */
    @region #region1, #region2 {
        div {...}
        p {...}
    }
    
    /* region style "RSB" */
    @region #region1 {
        p {...}
    }
        
</style>

<div id="div_1">
    <p id="p_1">...</p>
    <p id="p_2">...</p>
</div>

<div id="region1"></div>
<div id="region2"></div>
        

•  div div_1
•  paragraph p_1
•  paragraph p_2
•  range of flow that fits into region_1
•  range of flow that fits into region_2

The region style ‘RSA’ applies to flow content that is laid out in either ‘region_1’ or ‘region_2’.

The first rule set ‘div {...}’ applies to all <div> elements that fit partially or fully into ‘region_1’ or ‘region_2’. div_1 is split between ‘region_1’ and ‘region_2’ and gets the style from this style rule.

The second rule set ‘p {...}’ applies to all <p> elements that fit into ‘region_1’ or ‘region_2’. In our example, both p_1 and p_2 are selected.

The region style ‘RSB’ applies to flow content that fits in ‘region_1’.

The first rule set ‘p {...}’ matches p_1 and p_2 because these paragraphs flow into ‘region_1’. Only the segment of p_2 that flows into region_1 is styled with this rule.

The specificity of the selectors in a ‘@region’ rule is calculated as defined in the CSS Selectors module (see [SELECT]). In other words, the ‘@region’ rule adds an extra condition to the selector's matching, but does not change the selector's specificity. This is the same behavior as selectors appearing in ‘@media’ rules declaration blocks (see [MEDIAQ]), where the rule does not influence the selectors' specificity.

Consequently, selectors that match a given element (as describe above), participate in the CSS Cascading order as defined in [CSS21].

5. Pseudo-elements

It can be useful to visually mark the content to highlight that a content thread is flowing from region to region. For example, a marker such as ‘continues on page 3’ clearly indicates, at the end of a region, that there is more content in the flow which can be found on ‘page 3’ (in this example, the notion of page is application specific).

The ‘::before’ and ‘::after’ pseudo-elements (see [SELECT]) let content authors mark the beginning and end of a region with such markers.

5.1. Processing model

The ‘::before’ content is laid out in the region prior to any other content coming from the flow. Note that it is possible to set the ‘::before’ pseudo-element's ‘display’ property to ‘run-in’ to align it with the content's inline boxes.

The ‘::after’ content is laid out in the region after laying out the flow content. Then, flow content is removed from the region to accommodate for the ‘::after’ content. Accommodating means that the ‘::after’ content is laid out without overflowing the region. If there is still not enough room to accommodate for the ‘::after’ content after removing all flow content, then the ‘::after’ content overflows. The ‘display’ property of the ‘::after’ content can be set to ‘run-in’ to align with the region's content's inline boxes. In that case, the ‘::after’ content becomes the last inline box of the previous element in the flow that has some visual rendering in the region and can accommodate for the ‘::after’ box.

6. CSSOM view and CSS regions

Since content may flow into multiple regions, authors need a way to determine if there are enough regions to flow all the content from a named flow. This is especially important considering that the size of regions may change depending on the display context. For example, flowing the same content on a mobile phone with a small screen may require more regions than on a large desktop display.

Another example where creating more regions might be needed: if the user may change the font size of text flowing through regions, new regions may be needed to accommodate for the additional space required to fit the larger text or some regions may need to be removed for smaller text.

6.1. The NamedFlow interface

Supplemental methods on the Document interface provide access to named flows.

[Supplemental] interface Document {
  NamedFlow getFlowByName(DOMString name);
  NamedFlowCollection getNamedFlows();
};               

The getNamedFlows method on the Document interface returns the list of all the named flows in the document.

The getFlowByName method on the Document interface provides access to the document's named flow instances.

The NamedFlowCollection interface provides a list of current NamedFlow instances in the document. The collection is live and methods operate on the underlying data, not a snapshot of the data.

interface NamedFlowCollection {
    readonly attribute unsigned long length;
    caller getter NamedFlow item (in unsigned long index);
}
    

The length attribute returns the number of items in the collection.

The item(index) method returns the item at index index in the collection or null if index is out of range.

The NamedFlow interface offers a representation of the named flow.

interface NamedFlow {
  readonly attribute DOMString name;
  readonly attribute boolean overflow;
  readonly attribute NodeList contentNodes;
  NodeList getRegionsByContentNode(Node node);
};

The name attribute returns the name of the NamedFlow instance.

The overflow attribute returns true if the named flow does not fully fit in the associated regions. Otherwise, it returns false. A NamedFlow object is live.

The contentNodes attribute returns an ordered collection of nodes that constitute the named flow. Note that this collection is live: every time it is queried it must return the same object, and the object is always up to date.

The getRegionsByContentNode() method gets a collection of regions that contain at least part of the target content node. The returned NodeList is live: every time the method is called with the same node argument, it must return the same object, and the object is always up to date.This can be used to navigate by bookmark in paginated view: the method returns regions containing the bookmarked element, which are then passed to pagination UI to show desired region or page.

With the NamedFlow interface, authors can easily check if all content has been fitted into existing regions. If it has, the overflow property would be false.

6.2. Extension to the Element interface

When an region is an actual element, it is convenient to easily find out if content fully fits into the region or not. The supplemental interface on Element provides that functionality.

[Supplemental] interface Element {
    readonly attribute DOMString regionOverflow;
    getter Range[] getRegionFlowRanges();
};               
    

The regionOverflow attribute returns one of the following values:

‘overflow’

the region is the last one in the region chain and not able to fit the remaining content from the named flow. Note that the region's overflow property value can be used to control the visibility of the overflowing content.

‘fit’

the region element's content fits into the region's content box. It does not overflow. If the region is the last one in the region chain, it means that the content fits without overflowing. If the region is not the last one in the region chain, that means the named flow content is further fitted in subsequent regions. In particular, in this last case, that means the region may have received no content from the named flow (for example if the region is too small to accommodate any content).

‘empty’

the region element has no content and is empty. All content from the named flow was fitted in regions with a lower document order.

‘undefined’

The element is not a region.

Note that if there is no content in the named flow, all regions associated with that named flow should have their ‘overflow’ attribute return ‘empty’. If there is content in the flow but that content does not generate any box for visual formatting, the ‘overflow’ attribute on the first region in the region chain associated with the flow will return ‘fit’.

The getRegionFlowRanges method returns an array of Range instances corresponding to the content from the region flow that is positioned in the region.

If an element is not a region, the getRegionFlowRanges method throws a DOMException with the INVALID_ACCESS_ERR error code.

6.3. Region flow layout events

Region Event Targets dispatch regionLayoutUpdate events when there is a possible layout change of their named flow segment.

7. Relation to other specifications

This specification is related to other specifications as described in the references section. In addition, it is related to the following specifications:

1. CSS Exclusions Module [CSS3-EXCLUSIONS]. This module defines a generic way to define arbitrarily shaped exclusions into which content can flow or around which content can flow. This can be seen as an extension to the way CSS floats provide rectangular areas into which content flows and around which content flows. In advanced layout designs, it is expected that the CSS Exclusions module will be commonly combined with the CSS regions module.
2. CSS Line Grid Module [CSS3-LINE-GRID]. This module defines a concept of line grid to align the position of lines in different elements. The line grid functionality is related and needed for aligning content flowing in separate regions.

8. Use Cases

Use cases are described on this page.

9. Conformance

10. Changes

10.1. Changes from November 29^th 2011 version

• Modified region styling examples to use element selector instead of of pseudo-code selectors (this had been omitted in the previous pass at removing pseudo-code from the examples).
• Removed divs with class set to "issue moved", "issue stale" and "issue resolved" since these divs where not displayed.
• Minor updates to the alternate stylesheet.
• Removed "This section is normative" paragraphs since in CSS specifications, sections are normative unless otherwise specified.
• Removed "This section is informative" paragraphs since in CSS specifications notes are always informative.
• Reworded the text about flow-into: <ident> and removed obsolete text about the interaction with the ‘content’ property.
• Removed "this section is non-normative" from the "Regions Concepts" section.
• In the section on region breaks, removed descriptions of break values normatively defined in external specifications. Removed the section about split boxes and replaced with paragraph referencing the page breaking behavior. Removed the discussion about how the ‘overflow’ property applies to content flown in regions from the break section, since this is covered in the section on ‘region-overflow’ already. See mailing list feedback.
• Clarified that @region style rules only apply to the ‘portion’ of an element that falls into the corresponding region and added an issue that the model for ‘partial’ styling needs to be defined. See mailing list feedback.
• Clarified that the NodeList returned by getRegionsByContentNode is live.
• Added a name property to the NamedFlow interface. Added a NamedFlowCollection interface and added a getNamedFlows method on the Document interface, as per Bug 15828.
• Modified wording about containing block resolution for absolutely positioned elements in a named flow.
• Modified initial examples as per Bug 15131
• Multiple editorial changes following mailing list review comments

10.2. Changes from June 09^th 2011 version

• Editorial changes (typos, rephrasings).
• Made ‘content-order’ a <integer> and not a <float> following a working group resolution
• Added Alex Mogilevsky as an editor
• Flow names became <ident> instead of <string> following a working group resolution
• Removed issue about possibly altering the DOM Events model for region events following a working group resolution
• Made the "relation to document events" section informative following a working group resolution
• Removed issue in section "The NamedFlow interface" following the working group's resolution to have both NamedFlow and the Element interface extension
• Following a working group resolution:
  • Turned the first issue in the "Extensions to the Element interface" into a note explaining that the NamedFlow interface can be used when regions are pseudo-elements.
  • Added NamedFlowUpdate
• Excluded ‘none’, ‘inherit’ and ‘initial’ from the possible identifier names on the flow property following discussion on the mailing list.
• Simplified integration discussion on multi-column layout and just state that since column boxes are not addressable by selectors, they cannot be regions.
• Added specification of how the ‘flow-into’ property interacts with object, embed and iframe elements.
• Excluded ‘default’ from the possible identifier names on the flow property because it may get reserved.
• Added to the definition of ‘auto’ on ‘region-overflow’ specifying that region breaks must be ignored.
• Renamed ‘Document.flowWithName’ to ‘Document.getFlowByName’ since it is not a property.
• Added a note that a ‘NamedFlow’ instance is live.
• Added an ‘undefined’ string value to the regionOverflow property on the Element interface extension.
• Renamed NamedFlowEvent to regionLayoutUpdate to avoid having ‘Event’ in the event name.
• Added description for special behavior of iframe/object/embed as flow source
• Removed issue on copying content to a named flow instead of moving elements to named flow following working group resolution.
• Removed issue on content:flow-from v.s., flow-from property following working group resolution.
• Renamed ‘flow’ to ‘flow-into’ following working group resolution.
• Updated the css3-grid-align example following working group resolution that it should use <div> instead of grid-cell pseudo elements that were removed from the CSS Grid Layout specification.
• Renamed ‘from-flow’ to ‘flow-from’ following a working group resolution.
• Limited the applicability of ‘content: flow-from()’ to block container box and added a note that this might be expanded in the future, following a working group resolution.
• Removed issue about API to find which region displays an element in a named flow since ACTION-350 was created to add this API.
• In the ‘flow’ property description, removed the required wrapper anonymous block as agreed on mailing list discussion.
• Reworded the paragraph on how regions create a new stacking context, as per the mailing list discussion.
• Reworked the "CSS regions Model" section to now be "CSS regions Layout". Moved the definition of a region as the first sub-section.
• Removed the "Visual Formatting Model and Flows" section to match the new Regions Model (now CSS regions Layout) section.
• Moved the sections on allowed region breaks, forced region breaks and "best" regions breaks to follow the property definitions to follow the formatting of the paged media section in CSS 2.1.
• Added note about why regions create a new stacking context following the discussion on the mailing list.
• Removed sentence about content:none making elements disconnected following the discussion on the mailing list.
• Removed sentence about content:none making elements disconnected following the discussion on the mailing list.
• Added the ::region-before and a ::region-after pseudo-elements.
• Added note of caution when using selectors and the ‘flow-into’ property following a mailing list discussion.
• Removed sections about allowed, forced and best region breaks to align with the multi-column specification approach and until the group agrees on where and how the general issue of breaks (regions/pages/columns) should be addressed.
• Removed the section on Integration with other specifications since specifications that was superfluous especially since there is no specific integration with multi column, grid or template layout.
• Added a note that regions establish a new block formatting context.
• Renamed content-order to region-order.
• Added a note about overflowing content in regions (e.g., for content with borders).
• Added a note that a region cannot layout content it is part of (to avoid creating a circular dependency) in the flow-from description, specifying that if flow-from references the flow an element is part of, then the element does not format anything visually.
• Replaced ‘content:flow-from(<ident>)’ with ‘flow-from: <ident>’ following a working group resolution.
• Added more specific wording about auto width and auto height, following ACTION 351.
• Reworked section on region markers to now use ‘::before’ and ‘::after’ and explain how ‘display:run-in’ works with regions.
• Modified the @region style rule to remove the ::region-lines pseudo-selector.
• Removed the ‘region-order’ property following implementation feedback.
• Specified that region-overflow does not influence a region's size.
• Specified that the flow's writing mode is defined by the first region's writing mode following mailing list discussion.
• Made iframe, object and embed support of flow-into optional following mailing list discussion.
• Clarified that flow content following the last break in the last region is not rendered, following mailing list discussions.
• Modified the rule for computing the width and height of a region when they are set to auto, following a mailing list discussion.
• Added ‘auto’ to the list of invalid flow identifiers.
• Made ‘none’ the initial value for ‘flow-into’ and aligned with ‘flow-from’, as explained in this email. Also allowed the ‘inherit’ value on ‘flow-from’ and ‘flow-into’ (same email).
• Added note about nested region styling following a mailing list discussion.
• Added additional DOM interface following Action 350.
• Clarified that a region becomes a region only if its ‘content’ property computes to normal, following the resolution of Issue 22.
• Removed text about special iframe behavior as a result of ACTION 376.
• Made the selectors explicit in the initial section code examples, following discussion in San Jose, October 2011 face to face meeting.
• Added section on use cases following ACTION-377.

Acknowledgments

The editors are grateful to the CSS working group for their feedback and help with the genesis of this specification.

In addition, the editors would like to thank the following individuals for their contributions, either during the conception of CSS regions or during its development and specification review process:

• Rossen Atanassov
• Andrei Bucur
• Alexandru Chiculita
• Phil Cupp
• Arron Eicholz
• John Jansen
• Arno Gourdol
• David Hyatt
• Brian Heuston
• Ian Hickson
• Jonathan Hoersch
• Michael Jolson
• Brad Kemper
• Håkon Wium Lie
• Markus Mielke
• Robert O'Callahan
• Edward O'Connor
• Mihnea Ovidenie
• Virgil Palanciuc
• Olga Popiv
• Christoph Päper
• Anton Prowse
• Peter Sorotokin
• Alan Stearns
• Christian Stockwell
• Eugene Veselov
• Boris Zbarsky
• Stephen Zilles

References

Normative references

[CSS21]

Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607

[CSS3COL]

Håkon Wium Lie. CSS Multi-column Layout Module. 12 April 2011. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2011/CR-css3-multicol-20110412

[SELECT]

Tantek Çelik; et al. Selectors Level 3. 29 September 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-css3-selectors-20110929/

Other references

[CSS3-EXCLUSIONS]

Vincent Hardy; Rossen Atanassov. CSS Exclusions and Shapes Module Level 3. 13 December 2011. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2011/WD-css3-exclusions-20111213/

[CSS3-FLEXBOX]

Tab Atkins Jr.; Alex Mogilevsky; L. David Baron. CSS Flexible Box Layout Module. 29 November 2011. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2011/WD-css3-flexbox-20111129/

[CSS3-GRID-LAYOUT]

Alex Mogilevsky; et al. Grid Layout. 7 April 2011. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2011/WD-css3-grid-layout-20110407

[CSS3-LINE-GRID]

Koji Ishii. CSS Line Grid Module. Proposal for a CSS module. (Retrieved 26 October 2011) URL: http://dev.w3.org/csswg/css-line-grid/

[CSS3GRID]

Alex Mogilevsky; Markus Mielke. CSS Grid Positioning Module Level 3. 5 September 2007. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2007/WD-css3-grid-20070905

[CSS3LAYOUT]

Bert Bos; César Acebal. CSS Template Layout Module. 29 April 2010. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2010/WD-css3-layout-20100429

[CSS3PAGE]

Håkon Wium Lie; Melinda Grant. CSS3 Module: Paged Media. 10 October 2006. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2006/WD-css3-page-20061010

[DOM-LEVEL-2-TRAVERSAL-RANGE]

Joe Kesselman; et al. Document Object Model (DOM) Level 2 Traversal and Range Specification. 13 November 2000. W3C Recommendation. URL: http://www.w3.org/TR/2000/REC-DOM-Level-2-Traversal-Range-20001113

[MEDIAQ]

Håkon Wium Lie; et al. Media Queries. 27 July 2010. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2010/CR-css3-mediaqueries-20100727/

Index

• break-after, 4.3.
• break-before, 4.3.
• break-inside, 4.3.
• contentNodes, 6.1.
• current-region, 2.3.
• flow-from, 4.2.
• flow-into, 4.1.
• getRegionFlowRanges, 6.2.
• getRegionsByContentNode(), 6.1.
• item(index), 6.1.
• length, 6.1.
• name, 6.1.
• NamedFlow, 6.1.
• named flow, 2.2.
• NamedFlowCollection, 6.1.
• overflow, 6.1.
• region, 2.1.
• regionOverflow, 6.2.
• region-overflow, 4.4.
• specified flow, 4.1.

Property index