CSS Table Module Level 3

Editor’s Draft,

Specification Metadata
This version:
https://drafts.csswg.org/css-tables-3/
Latest published version:
https://www.w3.org/TR/css-tables-3/
Previous Versions:
Issue Tracking:
Inline In Spec
GitHub Issues
Editors:
Francois Remy (Microsoft)
Greg Whitworth (Microsoft)
Former Editors:
Bert Bos (W3C)
L. David Baron (Mozilla)
Markus Mielke (Microsoft)
Saloni Mira Rai (Microsoft)
Not Ready For Implementation

This spec is not yet ready for implementation. It exists in this repository to record the ideas and promote discussion.

Before attempting to implement this spec, please contact the CSSWG at www-style@w3.org.


Abstract

This CSS module defines a two-dimensional grid-based layout system, optimized for tabular data rendering. In the table layout model, each display node is assigned to an intersection between a set of consecutive rows and a set of consecutive columns, themselves generated from the table structure and sized according to their content.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, etc.

Status of this document

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.

GitHub Issues are preferred for discussion of this specification. When filing an issue, please put the text “css-tables” in the title, preferably like this: “[css-tables] …summary of comment…”. All issues and comments are archived, and there is also a historical archive.

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 document is governed by the 1 March 2017 W3C Process Document.

1. Introduction

This section is not normative

Many types of information (ex: weather readings collected over the past year) are best visually represented in a two-axis grid where rows represent one item of the list (ex: a date, and the various weather properties measured during that day), and where columns represent the successive values of an items property (ex: the temperatures measured over the past year).

Sometimes, to make the representation easier to understand, some cells of the grid are used to represent a description or summary of their parent row/column, instead of actual data. This happens more frequently for the cells found on the first row and/or column (called headers) or the cells found on the last row and/or column (called footers).

This kind of tabular data representation is usually known as tables. Tables layout can be abused to render other grid-like representations like calendars or timelines, though authors should prefer other layout modes when the information being represented does not make sense as a data table.

The rendering of tables in HTML has been defined for a long time in the HTML specification. However, its interactions with features defined in CSS remained for a long time undefined. The goal of this specification is to define the expected behavior of user agents supporting both HTML tables and CSS.

Please be aware that some behaviors defined in this document will not be the most logical or useful way of solving the problem they aim to solve, but such behaviors are often the result of compatibility requirements and not a deliberate choice of the editors of this specification. Authors wishing to use more complex layouts are encouraged to rely on more modern CSS modules such as CSS Grids.

2. Content Model

2.1. Table Structure

The CSS table model is based on the HTML4 table model, in which the structure of a table closely parallels the visual layout of the table. In this model, a table consists of an optional caption and any number of rows of cells.

In addition, adjacent rows and columns may be grouped structurally and this grouping can be reflected in presentation (e.g., a border may be drawn around a group of rows).

The table model is said to be "row primary" since authors specify rows, not columns, explicitly in the document language. Columns are derived once all the rows have been specified: the first cell of the first row belongs to the first column and as many other columns as spanning requires (and it creates them if needed), and the following cells of that row each belong to the next available column and as many other columns as spanning requires (creating those if needed); the cells of the following rows each belong to the next available column for that row (taking rowspan into account) and as many other columns as spanning requires (creating those if needed). (see §3.3 Dimensioning the row/column grid).

To summarize, an instance of the table model consists of:

Two representations of the structure of a table (tree vs layout)

The CSS model does not require that the document language include elements that correspond to each of these components. For document languages (such as XML applications) that do not have pre-defined table elements, authors must map document language elements to table elements. This is done with the display property.

The following display values assign table formatting rules to an arbitrary element:

table (equivalent to HTML: <table>)
Specifies that an element defines a block-level table: it is a rectangular block that participates in a block formatting context.
inline-table (equivalent to HTML: <table>)
Specifies that an element defines an inline-level table: it is a rectangular block that participates in an inline formatting context).
table-row (equivalent to HTML: <tr>)
Specifies that an element is a row of cells.
table-row-group (equivalent to HTML: <tbody>)
Specifies that an element groups some amount of rows.

Unless explicitly mentioned otherwise, mentions of table-row-groups in this spec also encompass the specialized table-header-groups and table-footer-groups.

table-header-group (equivalent to HTML: <thead>)
Like table-row-group but, for layout purposes, the first such row group is always displayed before all other rows and row groups.
If a table owns multiple display: table-header-group boxes, only the first is treated as a header; the others are treated as if they had display: table-row-group.
table-footer-group (equivalent to HTML: <tfoot>)
Like table-row-group but, for layout purposes, the fist such row group is always displayed after all other rows and row groups.
If a table owns multiple display: table-footer-group boxes, only the first is treated as a footer; the others are treated as if they had display: table-row-group.
table-column (equivalent to HTML: <col>)
Specifies that an element describes a column of cells.
table-column-group (equivalent to HTML: <colgroup>)
Specifies that an element groups one or more columns.
table-cell (equivalent to HTML: <td> or <th>)
Specifies that an element represents a table cell.
table-caption (equivalent to HTML: <caption>)
Specifies a caption for the table. Table captions are positioned between the table margins and its borders.

Authors should not assign a display type from the previous list to replaced elements (eg: input fields or images). When the display property of a replaced element computes to one of these values, it is handled instead as though the author had declared inline (for inline-table, table-cell, table-column) or block (for all other values). Whitespace collapsing and box generation must happen around those replaced elements like if they never had any other display type.

This is a breaking change from css 2.1 but matches implementations <https://github.com/w3c/csswg-drafts/issues/508>

2.1.1. Terminology

In addition to the table structure display types, the following wording is also being used in this spec:

table-wrapper box
An anonymous box generated around table-root boxes to account for any space occupied by each table-caption it owns.
table-root box or element
A table or inline-table box.
table-non-root box or element
A proper table child, or a table-cell box.
table-track box or element
A table-row, or table-column box.
table-track-group box or element
A table-row-group, or table-column-group box.
proper table child box or element
A table-track-group, table-track, or table-caption box.
proper table-row parent box or element
A table-root or a table-row-group box.
table-internal box or element
A table-cell, table-track or table-track-group box.
tabular container
A table-row or proper table-row parent box.
consecutive boxes
Two sibling boxes are consecutive if they have no intervening siblings other than, optionally, an anonymous inline containing only white spaces. A sequence of sibling boxes is consecutive if each box in the sequence is consecutive to the one before it in the sequence.
table grid
A matrix containing as many rows and columns as needed to describe the position of all the table-rows and table-cells of a table-root, as determined by the grid-dimensioning algorithm.

Each row of the grid might correspond to a table-row, and each column to a table-column.

slot of the table grid.
A slot (r,c) is an available space created by the intersection of a row r and a column c in the table grid.

Each slot of the table grid is covered by at least one table-cell (some of them anonymous), and at most two. Each table-cell of a table-root covers at least one slot.

Table-cells which cover more than one slot do so densely, meaning the set of slots they cover can always be described as a set of four strictly-positive integers (rowStart, colStart, rowSpan, colSpan) such that a slot (r,c) is covered by the table-cell if and only if r lies in the interval between rowStart (included) and rowStart+rowSpan (exculded), and c lies in the interval between colStart (included) and colStart+colSpan (exculded);

Such table-cell is said to originate from row rowStart and column colStart. Also:

  • A table-cell is said to originate a table-row (resp. table-column) if it originates its corresponding row (resp. column)
  • A table-cell is said to originate a table-row-group (resp. table-column-group) if the group contains the cell’s originating row (resp. column)

Such table-cell is said to span all rows r and columns c matching the above condition. Also:

  • A table-cell is said to span a table-row (resp. table-column) if it spans its corresponding row (resp. column)
  • A table-row (resp. table-column) corresponding to a row (resp. column) is said to span this row (resp. column)
  • A table-row (resp. table-column) is said to span all columns of the grid (resp. row)
  • A table-row-group (resp. table-column) containing a row (resp. column) is said to span the row (resp. column)
  • A table-row-group (resp. table-column) is said to span all columns of the grid (resp. row)

2.2. Fixup

Document languages other than HTML may not contain all the elements in the CSS 2.1 table model. In these cases, the "missing" elements must be assumed in order for the table model to work.

Any table-internal element will automatically generate necessary anonymous table objects around itself, if necessary. Any descendant of a table-root that is not table-internal must have a set of ancestors in the table consisting of at least three nested objects corresponding to a table/inline-table, a table-row, and a table-cell. Missing boxes cause the generation of anonymous boxes according to the following rules:

2.2.1. Fixup Algorithm

For the purposes of these rules, out-of-flow elements are represented as inline elements of zero width and height. Their containing blocks are chosen accordingly.

The following steps are performed in three stages:

  1. Remove irrelevant boxes:
    The following boxes are discarded as if they were display:none:
    1. Children of a table-column.
    2. Children of a table-column-group which are not a table-column.
    3. Anonymous inline boxes which contain only white space and are between two immediate siblings each of which is a table-non-root box.
    4. Anonymous inline boxes which meet all of the following criteria:
  2. Generate missing child wrappers:
    1. An anonymous table-row box must be generated around each sequence of consecutive children of a table-root box which are not proper table child boxes. !!Testcase
    2. An anonymous table-row box must be generated around each sequence of consecutive children of a table-row-group box which are not table-row boxes. !Testcase
    3. An anonymous table-cell box must be generated around each sequence of consecutive children of a table-row box which are not table-cell boxes. !Testcase
  3. Generate missing parents:
    1. An anonymous table-row box must be generated around each sequence of consecutive table-cell boxes whose parent is not a table-row. Testcase
    2. An anonymous table or inline-table box must be generated around each sequence of consecutive proper table child boxes which are misparented. If the box’s parent is an inline, run-in, or ruby box (or any box that would perform inlinification of its children), then an inline-table box must be generated; otherwise it must be a table box. Testcase Testcase !Testcase
    3. An anonymous table-wrapper box must be generated around each table-root. Its display type is inline-block for inline-table boxes and block for table boxes. The table wrapper box establishes a block formatting context. The table-root box (not the table-wrapper box) is used when doing baseline vertical alignment for an inline-table. The width of the table-wrapper box is the border-edge width of the table box inside it. Percentages which would depend on the width and height on the table-wrapper box’s size are relative to the table-wrapper box’s containing block instead, not the table-wrapper box itself.
Please note that some layout modes such as flexbox and grid override the display type of their children. These transformations happen before the table fixup.
Please note that the float and position properties sometimes affect the computed value of display. When those properties are used on what should have been table internal boxes, they switch to block instead. This transformation happen before the table fixup.
We have modified the text of this section from CSS 2.2 to make it easier to read. If you find any mistakes due to these changes please file an issue

2.2.2. Characteristics of fixup boxes

Beside their display type, the anonymous boxes created for fixup purposes do not receive any specific or default styling, except where otherwise mentioned by this specification.

This means in particular that their computed background is “transparent”, their computed padding is “0px”, their computed border-style is “none”.

It is also woth reminding that an anonymous box inherits property values through the box tree.

2.2.3. Examples

<div class="row">
  <div class="cell">George</div>
  <div class="cell">4287</div>
  <div class="cell">1998</div>
</div>

Here is the associated styles:

.row { display: table-row }
.cell { display: table-cell }

After fixup, this will produce layout boxes as though this was the initial HTML:

<table>
  <tr>
    <td>George</td>
    <td>4287</td>
    <td>1998</td>
  </tr>
</table>

In this example, three table-cell anonymous boxes are assumed to contain the text in the rows. The text inside of the divs with a display: table-row are encapsulated in anonymous inline boxes, as explained in visual formatting model:

<div class="inline-table">
  <div class="row">This is the top row.</div>
  <div class="row">This is the middle row.</div>
  <div class="row">This is the bottom row.</div>
</div>
.inline-table { display: inline-table; }
.row { display: table-row; }

This will produce layout boxes as though this was the initial HTML:

<table>
  <tr>
    <td>This is the top row.</td>
  </tr>
  <tr>
    <td>This is the middle row.</td>
  </tr>
  <tr>
    <td>This is the bottom row.</td>
  </tr>
</table>

3. Layout

3.1. Core layout principles

Unlike other block-level boxes, tables do not fill their containing block by default. When their width computes to auto, they behave as if they had fit-content specified instead. This is different from most block-level boxes, which behave as if they had stretch instead.

The min-content width of a table is the width required to fit all of its columns min-content widths and its undistributable spaces.

The max-content width of a table is the width required to fit all of its columns max-content widths and its undistributable spaces.

If the width assigned to a table is larger than its min-content width, the Available Width Distribution algorithm will adjust column widths in consequence.

This section overrides the general-purpose rules that apply to calculating widths described in other specifications. In particular, if the margins of a table are set to 0 and the width to auto, the table will not automatically size to fill its containing block. However, once the used value of width for the table is found (using the algorithms given below) then the other parts of those rules do apply. Therefore, a table can be centered using left and right auto margins, for instance.

3.2. Table layout algorithm

To layout a table, user agents must apply the following actions:

  1. Determine the number of rows/columns the table requires.
    This is done by executing the steps described in §3.3 Dimensioning the row/column grid.
  2. [A] If the row/column grid has at least one slot:
    1. Ensure each cell slot is occupied by at least one cell.
      This is done by executing the steps described in §3.4 Missing cells fixup.
    2. Compute the minimum width of each column.
      This is done by executing the steps described in §3.8 Computing table measures.
    3. Compute the width of the table.
      This is done by executing the steps described in §3.9.1 Computing the table width.
    4. Distribute the width of the table among columns.
      This is done by executing the steps described in §3.9.3 Distribution algorithm.
    5. Compute the height of the table.
      This is done by executing the steps described in §3.10.1 Computing the table height.
    6. Distribute the height of the table among rows.
      This is done by executing the steps described in §3.10.4 Distribution algorithm.

    [B] Else, an empty table is laid out:

    1. Compute the width of the table.
      This is done by returning the largest value of CAPMIN and the computed width of the table box (including borders and paddings) if it is definite (use zero otherwise).
    2. Compute the height of the table.
      This is done by returning the sum of all table-caption heights (their width being set to the table width, with margins taken into consideration appropriately) and the computed height of the table box (including borders and paddings) if it is definite (use zero otherwise).
  3. Assign to each table-caption and table-cell their position and size.
    This is done by running the steps of §3.11 Positioning of cells, captions and other internal table boxes.

The following schema describes the algorithm in a different way, to make it easier to understand.

Overview of the table layout algorithm. Not normative.

3.3. Dimensioning the row/column grid

Like mentioned in the Table structure section, how many rows and columns a table has can be determined from the table structure. Both dimensioning the row/column grid and assigning table-cells their slot(s) in that grid do require running the HTML Algorithms for tables.

3.3.1. HTML Algorithm

CSS Boxes that do not originate from an HTML table element equivalent to their display type need to be converted to their HTML equivalent before we can apply this algorithm, see below. There is no way to specify the span of a cell in css only in this level of the spec, the use of an HTML td element is required to do so.

Apply the HTML5 Table Formatting algorithm, where boxes act like the HTML element equivalent to their display type, and use the attributes of their originating element if and only if it is an HTML element of the same type (otherwise, they act like if they didnt’t have any attribute).

<ul class="table">
  <li><b>One</b><i>1</i></li>
  <li><b>Two</b><i>2</i></li>
  <li><b>Three</b><i>3</i></li>
</ul>
<style>
  ul.table { display: table; }
  ul.table > li { display: table-row; }
  ul.table > li > * { display: table-cell; }
</style>

produces the same row/column grid as

<table><tbody>
  <tr>
    <td></td>
    <td></td>
  </tr>
  <tr>
    <td></td>
    <td></td>
  </tr>
  <tr>
    <td></td>
    <td></td>
  </tr>
</tbody></table>
<!-- built using dom api, as this would be fixed by the html parser -->
<grid style="display: table">
  <row style="display: table-row">
    <th rowspan="2">1</th>
    <colgroup style="display: table-cell" span="2" colspan="2">2</colgroup>
  </row>
  <tr>
    <td>A</td>
    <td>B</td>
    <td>C</td>
  </tr>
</grid>

produces the same row/column grid as

<table>
  <tr>
    <th rowspan="2">1</th>
    <td>2</td>
  </tr>
  <tr>
    <td>A</td>
    <td>B</td>
    <td>C</td>
  </tr>
</table>

Note how the second cell of the first row doesn’t have ```colspan=2``` applied, because its originating element is not an HTML TD element.

Testcase. !!Testcase. !Test case. !!Test case. !!Test case.

3.3.2. Track merging

The HTML Table Formatting algorithm sometimes generates more tracks than necessary to layout the table properly. Those tracks have historically been ignored by user agents, so the next step just gets rid of them entirely to avoid dealing with them as exceptions later in the spec. We have tried to maintain the functionality with this change, but if you happen to find any issues due to this change please file an issue.

Modify iteratively the obtained grid by merging consecutive tracks as follows: As long as there exists an eligible track in the obtained row/column grid such that there is no table-column/table-row box defining the said track explicitly, and both the said track and the previous one are spanned by the exact same set of cells, those two tracks must be merged into one single track for the purpose of computing the layout of the table. Reduce the span of the cells that spanned the deleted track by one to compensate, and shift similarly the tracks from which cells originate when needed. (see spanning-ghost-rows test cases)

For tables in auto mode, every track is an eligible track for the purpose of the track-merging algorithm. For tables in fixed mode, only rows are eligible to be merged that way; which means that every column is preserved.

Finally, assign to the table-root grid its correct number of rows and columns (from its mapped element), and to each table-cell its accurate rowStart/colStart/rowSpan/colSpan (from its mapped element).

3.4. Missing cells fixup

The following section clarifies and extends the CSS 2.1 statement saying that missing cells are rendered as if an anonymous table-cell box occupied their position in the grid (a "missing cell" is a slot in the row/column grid that is not covered yet by any table-cell box).

Once the amount of columns in a table is known, any table-row box must be modified such that it owns enough cells to fill all the columns of the table, when taking spans into account. New table-cell anonymous boxes must be appended to its rows content until this condition is met.

3.5. Table layout modes

This section covers the flags which modify the way tables are being laid out. There are three major flags for table layout: table-layout, border-collapse, and caption-side. The border-collapse flag has an optional border-spacing parameter.

3.5.1. The Table-Layout property

Name: table-layout
Value: auto | fixed
Initial: auto
Applies to: table-root boxes.
Inherited: yes
Percentages: n/a
Media: visual
Computed value: as specified
Canonical order: per grammar
Animation type: discrete

A table-root is said to be laid out in fixed mode whenever the computed value of the table-layout property is equal to fixed, and the specified width of the table root is either a <length-percentage>, min-content or fit-content. When the specified width is not one of those values, or if the computed value of the table-layout property is auto, then the table-root is said to be laid out in auto mode.

When a table-root is laid out in fixed mode, the content of its table-cells is ignored for the purpose of width computation, the aggregation algorithm for column sizing considers only table-cells belonging to the first row track, such that layout only depends on the values explicitly specified for the table-columns or cells of the first row of the table; columns with indefinite widths are attributed their fair share of the remaining space after the columns with a definite width have been considered, or 0px if there is no remaining space (see §3.8.3 Computing Column Measures).

3.5.2. The Border-Collapse property

Name: border-collapse
Value: separate | collapse
Initial: separate
Applies to: table-root boxes.
Inherited: yes
Percentages: n/a
Media: visual
Computed value: as specified
Canonical order: per grammar
Animation type: discrete

When the border-collapse property has collapse as its value, the borders of adjacent cells are merged together such that each cell draws only half of the shared border. As a result, some other properties like border-spacing will not applied in this case (see §3.6.2 Overrides applying in collapsed-borders mode), (see §3.7 Border-collapsing).

A table-root is said to be laid out in collapsed-borders mode in this case. Otherwhise, the table-root is said to be laid out in separated-borders mode.

3.5.2.1. The Border-Spacing property
Name: border-spacing
Value: <​length​>{1,2}
Initial: 0px 0px
Applies to: table-root boxes when border-collapse is separate.
Inherited: yes
Percentages: n/a
Media: visual
Computed value: two absolute lengths
Canonical order: per grammar
Animatable: yes

The lengths specify the distance that separates adjoining cell borders in separated-borders mode, and must not be strictly negative.

If one length is specified, it gives both the horizontal and vertical spacing. If two are specified, the first gives the horizontal spacing and the second the vertical spacing.

See §3.8.1 Computing Undistributable Space for details on how this affects the table layout.

3.5.3. The Caption-Side property

Name: caption-side
Value: top | bottom
Initial: top
Applies to: table-caption boxes
Inherited: yes
Percentages: n/a
Media: visual
Computed value: as specified
Canonical order: per grammar
Animation type: discrete

This property specifies the position of the caption box with respect to the table box. Values have the following meanings:

top
Positions the caption box above the table box.
bottom
Positions the caption box below the table box.
CSS2 described a different width and horizontal alignment behavior. That behavior was supposed to be introduced in CSS3 using the values top-outside and bottom-outside. #REF
Gecko also supports the "left" and "right" values, but currently this specification is not attempting to define their implementation of said values.
Gecko has a bug when dealing with multiple captions. !Testcase

To align caption content horizontally within the caption box, use the text-align property.

In this example, the caption-side property places captions below tables. The caption will be as wide as the parent of the table, and caption text will be left-justified.

caption {
  caption-side: bottom;
    width: auto;
    text-align: left
}

3.6. Style overrides

Some css properties behave differently inside css tables. The following sections list the exceptions and their effects.

3.6.1. Overrides applying in all modes

The following rules apply to all tables, irrespective of the layout mode in use.

3.6.2. Overrides applying in collapsed-borders mode

When a table is laid out in collapsed-borders mode, the following rules apply:

3.7. Border-collapsing

This entire section is a proposal to make the rendering of collapsed borders sane. As implementations diverge very visibly, it is expected to require more discussion than some other parts. Since browsers handle this so differently, convergence cannot happen without reimplementation. A major concern for this proposal was to support as many cases as possible, and yet keep the effort required for a new implementation of tables as low as possible.

Background: CSS+HTML allow unprecedented combinations of border modes for table junctions, and it makes it difficult to support all cases properly; in fact some combinations are not well-posed problems, so no rendering algorithm could be optimal.

Because they grew from something simple (HTML) to something very complex (HTML+CSS), the current table rendering models (backgrounds and borders) used by web browsers are insane (in the sense they are buggy, not interoperable and not CSSish at all). Many usual CSS assumptions are broken, and renderings diverge widely.

This proposal aims at fixing this situation.

border-collapsing breaking change from 2.1 <https://github.com/w3c/csswg-drafts/issues/604>

3.7.1. Conflict Resolution for Collapsed Borders

When they are laid out in collapsed-borders mode, table-root and table-cell boxes sharing a border attempt to unify their borders so that they render using the same style, width, and color (whenever this is possible). This is accomplished by running the following algorithm.

3.7.1.1. Conflict Resolution Algorithm for Collapsed Borders
For the purpose of this algorithm, “harmonizing” a set of borders means applying the “Harmonization Algorithm for Collapsed Borders” on the given set of borders, and set those borders' used values to the value resulting from the algorithm, except for cells having a border-image-source different from none: those keep their initial values.

For any table-cell C° of a table-root:

  • Divide the used width of all borders by two.
    This effect will be compensated at rendering time wherever needed, but is required for layout correctness. (see §5.3.3.1 Changes in collapsed-borders mode)

    Then, for that table-root:

    Implementations may of course choose to skip some of the steps of the previous algorithm, provided they can prove those have no visible impact on the final results; certain borders are harmonized more than once using the previous steps, but preventing this would make the spec harder to read.
    To help the reader get a better idea of what this algorithm is doing, the main steps of applying the previous algorithm over a sample table have been outlined here:

    https://jsfiddle.net/bn3d1sm4/
    https://jsfiddle.net/bn3d1sm4/1/
    https://jsfiddle.net/bn3d1sm4/2/

    https://jsfiddle.net/bn3d1sm4/15/
    3.7.1.2. Harmonization Algorithm for Collapsed Borders
    For the purpose of this algorithm, “considering” a border’s properties means that “if its properties are more specific than CurrentlyWinningBorderProperties, set CurrentlyWinningBorderProperties to its properties”.

    Change specificity in harmonization of collapsed borders? <https://github.com/w3c/csswg-drafts/issues/606>

    Given an ordered set of border styles (BC1, BC2, … located in cells C1, C2, …) execute the following algorithm to determine the used value of the border properties for those conflicting borders.

    3.7.1.3. Specificity of a border style

    Given two borders styles, the border style having the most specificity is the border style which…

    1. … has the value "hidden" as border-style, if only one does
    2. … has the biggest border-width, once converted into css pixels
    3. … has the border-style which comes first in the following list:
      double, solid, dashed, dotted, ridge, outset, groove, inset, none

    If none of these criterion matches, then both borders share the same specificity.

    3.8. Computing table measures

    3.8.1. Computing Undistributable Space

    The undistributable space of the table is the sum of the distances between the borders of consecutive table-cells (and between the border of the table-root and the table-cells).

    The distance between the borders of two consecutive table-cells is the border-spacing, if any.

    The distance between the table border and the borders of the cells on the edge of the table is the table’s padding for that side, plus the relevant border spacing distance (if any).

    For example, on the right hand side, the distance is padding-right + horizontal border-spacing.

    3.8.2. Computing Cell Measures

    The following terms are parameters of tables or table cells. These parameters encapsulate the differences between tables with different values of border-collapse (separate or collapse) so that the remaining subsections of this section do not need to refer to them differently.

    cell intrinsic offsets
    The cell intrinsic offsets is a term to capture the parts of padding and border of a table cell that are relevant to intrinsic width calculation. It is a set of computed values for border-left-width, padding-left, padding-right, and border-right-width (along with zero values for margin-left and margin-right) defined as follows:
    • In separated-borders mode: the computed horizontal padding and border of the table-cell
    • In collapsed-borders mode: the computed horizontal padding of the cell and, for border values, the used border-width values of the cell (half the winning border-width)
    table intrinsic offsets
    The table intrinsic offsets capture the parts of the padding and border of a table that are relevant to intrinsic width calculation. It is a set of computed values for border-left-width, padding-left, padding-right, and border-right-width (along with zero values for margin-left and margin-right) defined as follows:

    The margins are not included in the table intrinsic offsets because handling of margins depends on the caption-side property.

    Handling of intrinsic offsets when in border collapsing mode <https://github.com/w3c/csswg-drafts/issues/608>

    total horizontal border spacing
    The total horizontal border spacing is defined for each table:
    • For tables laid out in separated-borders mode containing at least one column, the horizontal component of the computed value of the border-spacing property times one plus the number of columns in the table
    • Otherwise, 0
    offsets-adjusted min-width, width, and max-width
    • For table-track and table-track-group boxes, the offsets-adjusted value of width properties is their computed value, irrespective of the value of box-sizing applied on the element.
    • For table-cell boxes, the offsets-adjusted value of width properties is their computed value from which the cell’s border-{left|right}-width and/or padding-{left|right} have eventually been deduced, depending on the value of box-sizing.
      When the table is laid out in collapsed-borders mode, the border value to deduce is half the value of the winning border value on each side (see conflict resolution explaination note)

    Testcase. Testcase. Testcase.

    outer min-content and outer max-content widths
    The outer min-content and max-content widths are defined for table cells, columns, and column groups. The width, min-width, and max-width values used in these definitions are the offsets-adjusted values defined above:
    percentage contributions
    The percentage contribution of a table cell, column, or column group is defined in terms of the computed values of width, max-width, and min-width that have computed values that are percentages:

    max(percentage min-width, min(percentage width, percentage max-width)).

    If the computed values are not percentages, then 0% is used for width or min-width,and an infinite percentage is used for max-width.

    3.8.3. Computing Column Measures

    This subsection defines three important values associated with each column of a table: their min-content width (the smallest possible width attributed to this column), their max-content width (the width that would be attributed to the column if no other constraint applied), their intrinsic percentage width (the percentage of the table width the column desires to get, and could end up overriding its max-content width).

    To compute these values, an iterative algorithm is used. First, these values are computed ignoring any cell spanning more than one column. Then, these values are updated by taking into account cells spanning incrementally more columns. When cells that spanned all columns of the table have been considered, this algorithm ends and the values are then finalized.

    For the purpose of measuring a column when laid out in fixed mode, only cells which originate in the first row of the table (after reordering the header and footer) will be considered, if any. In addition, the min-content and max-content width of cells is considered zero unless they are directly specified as a length-percentage, in which case they are resolved based on the table width (if it is definite, otherwise use 0).

    For the purpose of calculating the outer min-content width of cells, descendants of table cells whose width depends on percentages of their parent cell' width are considered to have an auto width. Testcase Testcase

    min-content width of a column based on cells of span up to 1
    The largest of:
    max-content width of a column based on cells of span up to 1
    The largest of:
    intrinsic percentage width of a column based on cells of span up to 1
    The largest of the percentage contributions of each cell that spans the column whose colSpan is 1, of its corresponding table-column (if any), and of its corresponding table-column-group (if any)
    min-content width of a column based on cells of span up to N (N > 1)
    the largest of the min-content width of the column based on cells of span up to N-1 and the contributions of the cells in the column whose colSpan is N, where the contribution of a cell is the result of taking the following steps:
    1. Define the baseline min-content width as the sum of the max-content widths based on cells of span up to N-1 of all columns that the cell spans.
    2. Define the baseline border spacing as the sum of the horizontal border-spacing for any columns spanned by the cell, other than the one in which the cell originates.
    3. The contribution of the cell is the sum of:
      • the min-content width of the column based on cells of span up to N-1
      • the product of:
        • the ratio of:
          • the max-content width of the column based on cells of span up to N-1 of the column minus the min-content width of the column based on cells of span up to N-1 of the column, to
          • the baseline max-content width minus the baseline min-content width
          or zero if this ratio is undefined, and
        • the outer min-content width of the cell minus the baseline min-content width and the baseline border spacing, clamped to be at least 0 and at most the difference between the baseline max-content width and the baseline min-content width
      • the product of:
        • the ratio of the max-content width based on cells of span up to N-1 of the column to the baseline max-content width
        • the outer min-content width of the cell minus the baseline max-content width and baseline border spacing, or 0 if this is negative
    max-content width of a column based on cells of span up to N (N > 1)
    The largest of the max-content width based on cells of span up to N-1 and the contributions of the cells in the column whose colSpan is N, where the contribution of a cell is the result of taking the following steps:
    1. Define the baseline max-content width as the sum of the max-content widths based on cells of span up to N-1 of all columns that the cell spans.
    2. Define the baseline border spacing as the sum of the horizontal border-spacing for any columns spanned by the cell, other than the one in which the cell originates.
    3. The contribution of the cell is the sum of:
      • the max-content width of the column based on cells of span up to N-1
      • the product of:
        • the ratio of the max-content width based on cells of span up to N-1 of the column to the baseline max-content width
        • the outer max-content width of the cell minus the baseline max-content width and the baseline border spacing, or 0 if this is negative
    intrinsic percentage width of a column based on cells of span up to N (N > 1)
    If the intrinsic percentage width of a column based on cells of span up to N-1 is greater than 0%, then the intrinsic percentage width of the column based on cells of span up to N is the same as the intrinsic percentage width of the column based on cells of span up to N-1.

    Otherwise, it is the largest of the contributions of the cells in the column whose colSpan is N, where the contribution of a cell is the result of taking the following steps:
    1. Start with the percentage contribution of the cell.
    2. Subtract the intrinsic percentage width of the column based on cells of span up to N-1 of all columns that the cell spans. If this gives a negative result, change it to 0%.
    3. Multiply by the ratio of
      • the column’s non-spanning max-content width to
      • the sum of the non-spanning max-content widths of all columns spanned by the cell that have an intrinsic percentage width of the column based on cells of span up to N-1 equal to 0%.
      However, if this ratio is undefined because the denominator is zero, instead use the 1 divided by the number of columns spanned by the cell that have an intrinsic percentage width of the column based on cells of span up to N-1 equal to zero.
    min-content width of a column
    the min-content width of the column based on cells of span up to N, where N is the number of columns in the table
    max-content width of a column
    the max-content width of the column based on cells of span up to N, where N is the number of columns in the table
    intrinsic percentage width of a column
    the smaller of:
    • the intrinsic percentage width of the column based on cells of span up to N, where N is the number of columns in the table
    • 100% minus the sum of the intrinsic percentage width of all prior columns in the table (further left when direction is "ltr" (right for "rtl")) Testcase

    The clamping of the total of the intrinsic percentage widths of columns to a maximum of 100% means that the table layout algorithm is not invariant under switching of columns.

    constrainedness
    A column is constrained if the column group (if any), the column (if any), or any of the cells spanning only that column has a computed width that is not "auto", and is not a percentage.
    In a future revision of this specification, this algorithm will need to account for character-alignment of cells ('<string>' values of the text-align property). This requires (based on the 9 March 2011 editor’s draft of css3-text) separately tracking max-content widths for the part of the column before the center of the alignment string and the part of the column after the center of the alignment string. For tracking min-content widths, there are two options: either not track them, or track three values: two values as for max-content widths for any cells that do not have break points in them, and a fourth value for any cells that do have break points in them (and to which character alignment is therefore not mandatory).
    EDITORIAL. The way this describes distribution of widths from colspanning cells is wrong. For min-content and max-content widths it should refer to the rules for distributing excess width to columns for intrinsic width calculation.

    3.9. Available Width Distribution

    3.9.1. Computing the table width

    Before deciding on the final width of all columns, it is necessary to compute the width of the table itself.

    As noted before, this would usually be the sum of preferred width of all columns, plus any extra. In this case, the width distribution will result in giving each column its preferred width. There are however a few cases where the author asks for some other width explicitly, as well as a few cases where the table cannot be given the width it requires.

    The caption width minimum (CAPMIN) is the largest of the table captions min-content contribution.

    The row/column-grid width minimum (GRIDMIN) width is the sum of the min-content width of all the columns plus cell spacing or borders.

    The row/column-grid width maximum (GRIDMAX) width is the sum of the max-content width of all the columns plus cell spacing or borders.

    The used width of a table depends on the columns and captions widths as follows:

    The assignable table width is the used width of the table minus the total horizontal border spacing (if any). This is the width that we will be able to allocate to the columns.

    In this algorithm, rows (and row groups) and columns (and column groups) both constrain and are constrained by the dimensions of the cells they contain. Setting the width of a column might indirectly influence the height of a row, and vice versa.

    3.9.2. Core distribution principles

    This section is not normative.

    3.9.2.1. Rules

    Ideally, each column should get its preferred width (usually its max-content width). However, the assignable table width calculated before could be either too big or too small to achieve this result, in which case the user agent must assign adhoc widths to columns as described in the width distribution algorithm.

    This algorithm follows three rules when determining a column’s used width:

    Rule 0: In fixed mode, auto and percentages columns are assigned a minimum width of zero pixels, and percentage resolution follows a different set of rules, whose goal is to ensure pixel columns always get assigned their preferred width.

    Rule 1: When assigning preferred widths, specified percent columns have a higher priority than specified unit value columns, which have a higher priority than auto columns.

    Rule 2: Columns using the same sizing type (percent columns, pixel columns, or auto columns) follow the same distribution method. For example, they all get their min-content width or they all get their max-content width.
    There is one exception to this rule. When giving its preferred percent width to a percent-column, if that would result in a size smaller than its min-content width, the column will be assigned its min-content width instead though the percent-columns group as a whole is still regarded as being assigned the preferred percent widths.

    Rule 3: The sum of width assgined to all columns should be equal to the assignable table width.

    3.9.2.2. Available sizings

    All three types of columns have the following possible used widths.

    1. min-content width:
      The size required to fit the content of the column
    2. min-content width + delta:
      A value between the min-content and preferred widths
    3. preferred width:
      The size specified for the column, or the size required to fit the content of the column without breaking
    4. preferred width + delta
      A value larger than the preferred width

    The distribution algorithm defines those values and explains when to use them.

    3.9.3. Distribution algorithm

    When a table is laid out at a given used width, the used width of each column must be determined as follows, eventually after considering the changes to this algorithm applied in fixed mode.

    First, each column of the table is assigned a sizing type:

    Then, valid sizing methods are to be assigned to the columns by sizing type, yielding the following sizing-guesses:

    1. The min-content sizing-guess is the set of column width assignments where each column is assigned its min-content width.
    2. The min-content-percentage sizing-guess is the set of column width assignments where:
      • each percent-column is assigned the larger of:
        • its intrinsic percentage width times the assignable width and
        • its min-content width.
      • all other columns are assigned their min-content width.
    3. The min-content-specified sizing-guess is the set of column width assignments where:
      • each percent-column is assigned the larger of:
        • its intrinsic percentage width times the assignable width and
        • its min-content width
      • any other column that is constrained is assigned its max-content width
      • all other columns are assigned their min-content width.
    4. The max-content sizing-guess is the set of column width assignments where:
      • each percent-column is assigned the larger of:
        • its intrinsic percentage width times the assignable width and
        • its min-content width
      • all other columns are assigned their max-content width.
    Note that:
    • The assignable table width is always greater than or equal to the table width resulting from the min-content sizing-guess.

    • The widths for each column in the four sizing-guesses (min-content, min-content-percentage, min-content-specified, and max-content) are in nondecreasing order.

    If the assignable table width is less than or equal to the max-content sizing-guess, the used widths of the columns must be the linear combination (with weights adding to 1) of the two consecutive sizing-guesses whose width sums bound the available width.

    Otherwise, the used widths of the columns are the result of starting from the max-content sizing-guess and distributing the excess width to the columns of the table according to the rules for distributing excess width to columns (for used width).

    The following schema describes the algorithm in a different way, to make it easier to understand.

    Legend

    Sizing algorithms: Each drawing of the table represents a way of sizing the columns. The four cases on the left are the sizing-guesses described above in the spec: min-content, min-content-percentage, min-content-specified, and max-content. The cases on the right are interpolations required for available sizes that do not match exactly one of the four sizing-guesses.

    Choice of sizing method: The sizing method selection always starts at the min-content sizing-guess (top left), and then proceeds by comparing the available width and the width consumed by the method currently in use. Green arrows indicate the direction you should follow if you have extra space to distribute after applying the current method. Red arrows indicate the direction you should follow if you have distributed too much space by applying the current method and need to backtrack.

    Columns types: Each type of column (auto, px, %) has its own color in the schema (yellow, blue, orange). In an interpolation: columns that get shrinked down from their size in previous sizing-guess are repainted red, and columns that get expanded from their size in previous sizing-guess are repainted green.

    Overview of the width distribution algorithm. Not normative.

    Should min-width support percentages? <https://github.com/w3c/csswg-drafts/issues/607>

    3.9.3.1. Changes to width distribution in fixed mode

    The following changes to previous algorithm apply in fixed mode:

    3.9.3.2. Distributing excess width to columns

    The rules for distributing excess width to columns can be invoked in two ways:

    The rules for these two cases are largely the same, but there are slight differences.

    The remainder of this section uses the term distributed width to refer to the one of these widths that is being distributed, and the excess width is used to refer to the amount by which the width being distributed exceeds the sum of the distributed widths of the columns it is being distributed to.

    1. If there are non-constrained columns that have originating cells with intrinsic percentage width of 0% and with nonzero max-content width (aka the columns allowed to grow by this rule), the distributed widths of the columns allowed to grow by this rule are increased in proportion to max-content width so the total increase adds to the excess width.
    2. Otherwise, if there are non-constrained columns that have originating cells with intrinsic percentage width of 0% (aka the columns allowed to grow by this rule, which thanks to the previous rule must have zero max-content width), the distributed widths of the columns allowed to grow by this rule are increased by equal amounts so the total increase adds to the excess width.
    3. Otherwise, if there are (constrained) columns with intrinsic percentage width of 0% and with nonzero max-content width (aka the columns allowed to grow by this rule, which, due to other rules, must have originating cells), the distributed widths of the columns allowed to grow by this rule are increased in proportion to max-content width so the total increase adds to the excess width.
    4. Otherwise, if there are columns with intrinsic percentage width greater than 0% (aka the columns allowed to grow by this rule, which, due to other rules, must have originating cells), the distributed widths of the columns allowed to grow by this rule are increased in proportion to intrinsic percentage width so the total increase adds to the excess width.
    5. Otherwise, if there is any such column, the distributed widths of all columns that have originating cells are increased by equal amounts so the total increase adds to the excess width.
    6. Otherwise, the distributed widths of all columns are increased by equal amounts so the total increase adds to the excess width.
    These rules do not apply when the table is laid out in fixed mode. In this case, the simpler rules that follow apply instead:
    • If there are any columns with no width specified, the excess width is distributed in equally to such columns
    • otherwise, if there are columns with non-zero length widths from the base assignment, the excess width is distributed proportionally to width among those columns
    • otherwise, if there are columns with non-zero percentage widths from the base assignment, the excess width is distributed proportionally to percentage width among those columns
    • otherwise, the excess width is distributed equally to the zero-sized columns

    3.10. Available Height Distribution

    3.10.1. Computing the table height

    ?Testcase ?Testcase ?Testcase

    The height of a table is the sum of the row heights plus any cell spacing or borders. If the table has a height property with a value other than auto, it is treated as a minimum height for the table grid, and will eventually be distributed to the height of the rows.

    The minimum height of a row is the maximum of:

    ROWMIN is defined as the sum of the minimum height of the rows after a first row layout pass.

    Once the table height has been determined, a second row layout pass must happen to assign the correct minimum height to table rows, by taking percentages used in rows/cells specified height into account.

    Then, if the sum of the new heights of the table rows after this second pass is different from what is needed to fill the table height, the height distribution algorithm defined below is applied (either to size rows intermediately between their first minimum height and their new, or to increase the heights of rows beyond their new minimum height; in neither case, this will have an impact on the baseline of the rows).

    Once the final size of the table and the rows has been determined, the content of the table-cells must also go through a second layout pass, where, if appropriate, percentage-based heights are this time resolved against their parent cell used height.

    It is appropriate to resolve percentage heights on direct children of a table-cell if the cell is considered to have its height specified explicitly or the child is absolutely positioned, see CSS 2.

    It is further clarified that a cell is considered to have its height specified explicitly if the computed height of the cell or any of its table ancestors is a length or percentage, and that percentage does not behave as auto.

    It is possible that this second layout pass (where height percentages are being resolved) will make some cell contents overflow their parent cell. This is by design.

    3.10.2. Row layout

    The minimum height of a row (without spanning-related height distribution) is defined as the height of an hypothetical linebox containing the cells originating in the row and where cells spanning multiple rows are considered having a height of 0px (but their correct baseline). In this hypothetical linebox, cell heights are considered auto, but their other properties are conserved.

    For the purpose of calculating this height, descendants of table cells whose height depends on percentages of their parent cell' height are considered to have an auto height if they have overflow set to visible or hidden or if they are replaced elements, and a 0px height if they have not. Testcase !!Testcase

    The baseline of a cell is defined as the baseline of the first in-flow line box in the cell, or the first in-flow table-row in the cell, whichever comes first. If there is no such line box or table-row, the baseline is the bottom of content edge of the cell box.

    Here is how this works out in practice:

    td { vertical-align: baseline; outline: 3px solid silver; }
    img { float: left; clear: left; width: 32px; height: 32px; }
    img[title] { float: none; }
    
    <table><tr>
      <td>Baseline</td>
      <td>Baseline<table><tr><td>After</td></tr></table></td>
      <td><table><tr><td>Baseline</td></tr></table>After</td>
      <td><table align=right><tr><td>Before</td></tr></table><p>Baseline</p></td>
      <td><img src="http://w3.org/favicon.ico" /><p>Baseline</p></td>
      <td><img src="http://w3.org/favicon.ico" title="Baseline"/><br/><img src="http://w3.org/favicon.ico" title="After"/></td>
      <td><img src="http://w3.org/favicon.ico" /><img src="http://w3.org/favicon.ico" /></td>
    </tr></table>
    
    Rendering of this example in a compliant browser

    For the purposes of finding a baseline, in-flow boxes with a scrolling mechanisms (see the overflow property) must be considered as if scrolled to their origin position.

    The baseline of a cell may end up below its bottom border, see the example below.

    The cell in this example has a baseline below its bottom border:

    div { height: 0; overflow: hidden; }
    
    <table>
    <tr>
    <td>
    <div> Test </div>
    </td>
    </tr>
    </table>
    

    The vertical-align property of each table cell determines its alignment within the row. Each cell’s content has a baseline, a top, a middle, and a bottom, as does the row itself.

    In the context of table cells, values for vertical-align have the following meanings:

    baseline The baseline of the cell is aligned with the baseline of the other cells of the first row it spans (see the definition of baselines of cells and rows).
    top The top of the cell box is aligned with the top of the first row it spans.
    bottom The bottom of the cell box is aligned with the bottom of the last row it spans.
    middle The center of the cell is aligned with the center of the rows it spans.
    ... Other values do not apply to cells; the cell is aligned at the baseline instead.

    The maximum distance between the top of the cell box and the baseline over all cells that have 'vertical-align: baseline' is used to set the baseline of the row. If a row doesn’t have any cell that has 'vertical-align: baseline', the baseline of that row is the bottom content edge of the lowest cell in the row.

    The baseline of a table-root is the baseline of its first row, if any. Otherwise, it is the bottom content edge of the table-root.

    Testcase !!Testcase

    To avoid ambiguous situations, the alignment of cells proceeds in the following order:

    • First the cells that are aligned on their baseline are positioned. This will establish the baseline of the row.
    • Next the cells with 'vertical-align: top' are positioned. The row now has a top, possibly a baseline, and a provisional height, which is the distance from the top to the lowest bottom of the cells positioned so far.
    • If any of the remaining cells, those aligned at the bottom or the middle, have a height that is larger than the current height of the row, the height of the row will be increased to the maximum of those cells, by lowering the bottom.
    • Finally, assign their position to the remaining cells.

    Example showing how the previous algorithm creates the various alignment lines of a row.

    Diagram showing the effect of various values of vertical-align on table cells. Cell boxes 1 and 2 are aligned at their baselines. Cell box 2 has the largest height above the baseline, so that determines the baseline of the row.

    Since during row layout the specified heights of cells in the row were ignored and cells that were spanning more than one rows have not been sized correctly, their height will need to be eventually distributed to the set of rows they spanned. This is done by running the same algorithm as the column measurement, with the span=1 value being initialized (for min-content) with the largest of the resulting height of the previous row layout, the height specified on the corresponding table-row (if any), and the largest height specified on cells that span this row only (the algorithm starts by considering cells of span 2 on top of that assignment).

    EDITORIAL. Import the relevant section of §3.8.3 Computing Column Measures here.

    Rows that see their size increase as a result of applying these steps adjust by lowering their bottom.

    The cells whose position depended on the bottom of any updated row must be positioned correctly again in their respective rows.

    At this point, cell boxes that are smaller than the collective height of the rows they span receive extra top and/or bottom padding such that their content does not move vertically but their top/bottom edges meet the ones of the first/last row they span.

    Please note that heights being defined on row groups are being ignored by this algorithm

    3.10.3. Core distribution principles

    EDITORIAL. TODO. For current proposal, skip to §3.10.4 Distribution algorithm.
    Investigations on height distribution

    3.10.4. Distribution algorithm

    The first step is to attribute to each row its base size and its reference size.

    Its base size is the size it would have got if the table didn’t have a specified height (the one it was assigned when ROWMIN was evaluated).

    Its reference size is the largest of

    The second step is to compute the final height of each row based on those sizes.

    If the table height is equal or smaller than sum of reference sizes, the final height assigned to each row will be the weighted mean of the base and the reference size that yields the correct total height.

    Else, if the table owns any “auto-height” row (a row whose size is only determined by its content size and none of the specified heights), each non-auto-height row receives its reference height and auto-height rows receive their reference size plus some increment which is equal to the height missing to amount to the specified table height divided by the amount of such rows.

    Else, all rows receive their reference size plus some increment which is equal to the height missing to amount to the specified table height divided by the amount of rows.

    The cells whose position depended on the bottom of any updated row must be positioned correctly again in their respective rows.

    At this point, cell boxes that are smaller than the collective height of the rows they span receive extra top and/or bottom padding such that their content does not move vertically but their top/bottom edges meet the ones of the first/last row they span.

    3.11. Positioning of cells, captions and other internal table boxes

    We need a resolution on what visibility:collapse does. <https://github.com/w3c/csswg-drafts/issues/478>

    Once the width of each column and the height of each row of the table grid has been determined, the final step of algorithm is to assign to each table-internal box its final position.

    The table-wrapper box is then sized such that it contains the margin box of all table-non-root boxes as well as the table-root border-box.

    The position defined here is the position of the children inside the space reserved for the table-wrapper, which excludes only its margins. This is because the captions of the table are located outside the border-box area of the table-root.

    The position of any table-caption having "top" as caption-side within the table is defined as the rectangle whose:

    The position of any table-cell, table-track, or table-track-group box within the table is defined as the rectangle whose:

    Reminder: For table-track and table-track-group boxes, all tracks of the opposite direction to the grouping are considered spanned. For instance, a table-header-group is considered to span all the columns, and a table-column-group is considered to span all the rows.

    The position of any table-caption having "bottom" as caption-side within the table is defined as the rectangle whose:

    Cell overflow: If the table is laid out in fixed mode, if the content of some cell has grown more than the cell during its second layout pass or if some tracks spanned by visible cells are deemed not visible, the content of some cells may exceed the available space, and cause an overflow. Such overflow should behave exactly like if the cell was an absolutely positioned display:block box with the appropriate alignment in place to keep its content in place relative to its inline-start block-start corner (usually top left). !Testcase !Testcase Testcase
    Visible tracks: For the purpose of this algorithm, a column or row is considered a visible track if neither its corresponding table-track nor its table-track-group parent (if any) have visibility set to collapse.
    A table with a caption above it, showing how the caption margins are totally nested inside the table margins, but are outside the border-box of the table nonetheless.
    Diagram of a table with a caption above it.

    4. Absolute Positioning

    4.1. With a table-root as containing block

    If an absolutely positioned element’s containing block is generated by a table-wrapper box, the containing block corresponds to the area around which the table margins are applied, including the area where the table border is drawn and the margin area of any table-caption. The offset properties (top/right/bottom/left) then indicate offsets inwards from the corresponding edges of this containing block, as normal.

    Absolute positioning occurs after layout of the table and its in-flow contents, and does not contribute to the sizing of any table grid tracks or affect the size/configuration of the table grid in any way.

    The figure below shows how a box absolutely-positioned relative to a table should be rendred.

    The yellow area is the table content edge, yellow arrows the table margins.
    The green area is the table caption, green arrows the caption margins.
    The blue area is the table background area, and the darker blue area where the table border area.
    The black area is the descendant positioned relative to the table, the arrows represent the top/left/bottom/right displacements.

    4.2. With a table-internal as containing block

    If an absolutely positioned element’s containing block is generated by a table-internal, the containing block corresponds to the area starting at the top left corner of the the area that would be assigned to the box during layout but whose size is computed to be the one of the area that would be assigned to the box during layout if all tracks were considered visible (irrespective of visibility being set co collapse on some boxes), not including borders and paddings as appropriate.

    This is done so that hiding column does not trigger a layout in the absolutely-positioned boxes, and the content being clipped doesn’t seem to be moving. !!Testcase !!Testcase

    The offset properties (top/right/bottom/left) then indicate offsets inwards from the corresponding edges of this containing block, as normal.

    This only works in Firefox. It would make it easier to implement position:sticky in the future, though. [Chrome bug] [Interop risk: Firefox bug] <https://github.com/w3c/csswg-drafts/issues/858>

    4.3. With a table-internal box as non-containing block parent

    The only influence of non-containing block parent of an absolutely-positioned box is to define its static position, in case both top+bottom and/or left+right end up being auto.

    For table-cells, the absolutely-positioned content is positioned follows the rules for block layout as usual.

    Due to table fixup, it is not possible to create an absolutely-positioned box that is the child of a table-internal box that is not a table-cell (see note about float and position for more details).

    5. Rendering

    5.1. Paint order of cells

    Table cells are painted in a table-root in DOM order as usual, independently of where cells end up actually being drawn.

    5.2. Empty cell rendering (separated-borders mode)

    Name: empty-cells
    Value: show | hide
    Initial: show
    Applies to: table-cell boxes
    Inherited: yes
    Percentages: n/a
    Media: visual
    Computed value: as specified
    Canonical order: per grammar
    Animation type: discrete

    In collapsed-borders mode, this property has no effect.

    In separated-borders mode, when this property has the value hide, no borders or backgrounds are drawn around/behind empty cells.

    An empty cell is a table-cell containing neither:

    Can we simplify empty-cells:hide? <https://github.com/w3c/csswg-drafts/issues/605>

    For example, take the following markup and css:

    <table>
      <td><span></span></td>
      <td></td>
      <td><span></span></td>
    </table>
    
    table {
      width: 500px; height: 300px;
      empty-cells: hide;
    }
    
    table { background: black; border: 10px solid black; }
    td { background: white; }
    
    table { border-spacing: 0px; }
    td { padding: 0; }
    

    The correct rendering of this code snippet is depicted here:

    Rendering of three columns whose middle one is hidden by empty-cells:hide

    5.3. Drawing backgrounds and borders

    5.3.1. Drawing table backgrounds and borders

    Unlike other boxes types, table and inline-table boxes do not paint their background and borders around their entire client rect. Indeed, the table captions are to be visually positioned between the table margins and its borders, which means the drawing areas of various effects applied to the table-root need to be modified.

    Painting areas:

    This does not affect other uses of these concepts, like absolute positioning.

    !Testcase

    5.3.1.1. Changes in collapsed-borders mode

    When a table is laid out in collapsed-borders mode, the rendering of its borders on and those of its table-cells is modified. The following rules describe in which way.

    The rules for background and borders painting defined in §5.3 Drawing backgrounds and borders still apply if they are not overriden.

    Borders of a non-empty table-root are not painted in collapsed-borders mode, except if the border-image property is set.

    In this latter case, the border is drawn as if the table border was twice as big as its used value specify, and as if that excess was rendered inside the padding area of the table-root.

    Even if they are not drawn by the table, the table borders still occupy their space in the layout. Cells will render those shared borders.

    5.3.2. Drawing cell backgrounds

    Anonymous table-cells added by the missing cells fixup step do not render any of their backgrounds.

    In addition to its own background, table-cell boxes also render the backgrounds of the table-track and table-track-group boxes in which they belong. This is actually different from simply inheriting their background because the background-origin and background-size computations will actually be done on the bounds of the grouping boxes, and not on those of the cell.

    For the purposes of finding the background of each table cell, the different table boxes may be thought of as being on six superimposed layers. The background set in one of the layers will only be visible if the layers above it have a transparent background.

    Schema of table layers.

    1. The table background is being rendered by the table, and does not affect the cell background.
    2. The first background drawn by a cell is the background of its originating column group. For the purpose of background-positioning, it is expected that a column group occupies the largest possible area a single cell could occupy in the row/column grid while originating in the column group and not entering any column not part of the column group.
    3. The second background drawn by a cell is the background of its originating column. For the purpose of background-positioning, it is expected that a column occupies the largest possible area a single cell could occupy in the row/column grid while originating in the column and not entering any other column.
    4. The third background drawn by a cell is the background of its originating row group. For the purpose of background-positioning, it is expected that a row group occupies the largest possible area a single cell could occupy in the row/column grid while originating in the row group and not entering any row not part of the row group.
    5. The fourth background drawn by a cell is the background of its originating row. For the purpose of background-positioning, it is expected that a row occupies the largest possible area a single cell could occupy in the row/column grid while originating in the row and not entering any other row.
    6. The fifth background drawn by a cell is its own background. This is the one that appears on top once all backgrounds have been rendered.

    As the figure above shows, although all rows contain the same number of cells, not every cell may have specified content. In separated-borders mode, if the value of their empty-cells property is hide, these empty cells are not rendered at all, as if visibility: hidden was specified on them, letting the table background show through.

    5.3.3. Drawing cell borders

    In separated-borders mode, borders of table cells are rendered as usual.

    5.3.3.1. Changes in collapsed-borders mode

    Borders of a table-cell are rendered in collapsed-borders mode as if the cell border was twice as big as its used value specify, and as if that excess was rendered in the margin area of the cell, with the added constraint that for each side of the border which isn’t located at one of the table edges, the border is actually clipped to the border-box drawing area as its real used value define except if the border-image property is set.

    If applying the previously-mentioned clipping behavior results in clipping a border over a non-integer amount of device pixels, browsers may decide to snap the clipping area to a device pixel instead by ceiling the x- and y-values of the clipping area. Ceiling the values ensures that in a normal writing mode, the cell which gets the contested pixels between multiple cells is actually the most top left one, which has a greater specificity than the other ones according to this spec. See §5.1 Paint order of cells and §3.7.1.1 Conflict Resolution Algorithm for Collapsed Borders.

    5.3.4. Border styles (collapsed-borders mode)

    Some of the values of the border-style have different meanings for tables in collapsed-borders mode than usual. Those definitions override the default behavior for border-style values.

    hidden

    Same as none, but also inhibits any other border (see §3.7.1.3 Specificity of a border style).

    inset

    Same as ridge.

    outset

    Same as groove.

    5.4. Rendering for visibility: collapse

    When a table part has visibility: collapse set, the rendering is handled differently depending if it is on a table-cell, spanning table-cell, or a table-track/table-track-group.

    5.4.1. Rendering a visibility: collapse table cell

    As stated in CSS 2.2, if a table-cell has its visibility set to that of collapse, it is rendered the same as if it had visibility: hidden set.

    If the table-cell is spanning more than one table-track, and the table-track is set to visibility: collapse then clip the content to the table-cell’s border-box.

    5.4.2. Rendering a visibility: collapse table-track or table-track-group

    When a table-track or table-track-group has visibility: collapse, none of backgrounds, borders or outlines that are contributed by the cells within the given table-track or table-track-group are painted.

    6. Fragmentation

    6.1. Breaking across fragmentainers

    When fragmenting a table, user agents must attempt to preserve the table rows unfragmented if the cells spanning the row do not span any subsequent row, and their height is at least twice smaller than both the fragmentainer height and width. Other rows are said freely fragmentable.

    When a table doesn’t fit entirely in a fragmentainer, at least one row did fit entirely in the fragmentainer, and the first row that does not fit in the fragmentainer is not freely fragmentable. the user agent has to insert some vertical gap between the rows located before and at the overflow point such that the two rows end up separated in sibling fragmentainers. If the fragmentation requires repeating headers and footers, and the footer is repeated, then the footer must come directly after the last row in the fragmentainer and the vertical gap must be inserted after the repeated footer.

    Expected rendering of table fragmented across two pages

    When there is no row fitting entirely in the current fragmentainer or when the first row that does not fit in the fragmentainer is freely fragmentable, user agents must attribute all the remaining height in the fragmentainer to the cells of that row, and fit as much content as it can in each of the cells independently, then break to the next fragment and start the content of each cell where it was stopped in its previous fragment (top borders must not be repainted in continuation fragments).

    Expected rendering of table containing a tall row fragmented across two pages

    When break-before or break-after is applied to a table-row-group or a table-row box, the user agent has to insert some vertical gap between the rows located before and after the breaking point such that the two rows end up separated in sibling fragmentainers as required by the property value. If the fragmentation requires repeating headers and footers, and the footer is repeated, then the footer must come directly after the last row in the fragmentainer and the vertical gap must be inserted after the repeated footer.

    6.2. Repeating headers across pages

    When rendering the document into a paged media, user agents must repeat header rows and footer rows on each page spanned by a table if the page is the table’s fragmentainer, if the header/footer has avoid break-inside applied to it, if the height required to do so is inferior to two quarters of the page height (up to one quarter for header rows, and up to one quarter for footer rows), and if that doesn’t cause a row to be displayed twice on that page.

    When the header rows are being repeated, user agents must leave room and if needed render the table top border. The same applies for footer rows and the table bottom border.

    Expected rendering of table with headers and footers fragmented across two pages

    User agents may decide to extend this behavior to more fragmentation contexts, for instance repeat headers/rows across columns in addition to pages. User-agents that are rendering static documents are more likely to adopt this behavior, though this is not required per spec.

    7. Security Considerations

    Using CSS Tables does not incur any security risk to mitigate.

    8. Privacy Considerations

    Using CSS Tables does not incur any privacy risk to mitigate.

    9. List of bugs being tracked

    This section is not normative.

    10. Appendices

    10.1. Mapping between CSS & HTML attributes

    The default style sheet for HTML4 illustrates how its model maps to css properties and values:

    Some extensions to CSS have been used for contraints not mappable to current CSS constructs
      table    { display: table }
      thead    { display: table-header-group }
      tbody    { display: table-row-group }
      tfoot    { display: table-footer-group }
      tr       { display: table-row }
      td, th   { display: table-cell }
      colgroup { display: table-column-group }
      col      { display: table-column }
      caption  { display: table-caption }
      table, thead, tbody, tfoot, tr, td, th, colgroup, col, caption { box-sizing: border-box; }
      thead, tfoot { break-inside: avoid }
    
    Some of the content here came from the WHATWG spec on the HTML to CSS mapping of tables. However, since they include things which are not true in most browsers, this is not a simple copy. Investigations are therefore required for each and any merge being made from one source to another!

    11. (link here for missing sections)

  • Conformance

    Document conventions

    Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

    All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

    Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

    This is an example of an informative example.

    Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

    Note, this is an informative note.

    Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

    Conformance classes

    Conformance to this specification is defined for three conformance classes:

    style sheet
    A CSS style sheet.
    renderer
    A UA that interprets the semantics of a style sheet and renders documents that use them.
    authoring tool
    A UA that writes a style sheet.

    A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

    A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

    An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

    Requirements for Responsible Implementation of CSS

    The following sections define several conformance requirements for implementing CSS responsibly, in a way that promotes interoperability in the present and future.

    Partial Implementations

    So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported property values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

    Implementations of Unstable and Proprietary Features

    To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

    Implementations of CR-level Features

    Once a specification reaches the Candidate Recommendation stage, implementers should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec, and should avoid exposing a prefixed variant of that feature.

    To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

    Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

    Index

    Terms defined by this specification

    Terms defined by reference

    References

    Normative References

    [COMPOSITING-1]
    Rik Cabanier; Nikos Andronikos. Compositing and Blending Level 1. 13 January 2015. CR. URL: https://www.w3.org/TR/compositing-1/
    [CSS-BACKGROUNDS-3]
    Bert Bos; Elika Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. 17 October 2017. CR. URL: https://www.w3.org/TR/css-backgrounds-3/
    [CSS-BREAK-3]
    Rossen Atanassov; Elika Etemad. CSS Fragmentation Module Level 3. 9 February 2017. CR. URL: https://www.w3.org/TR/css-break-3/
    [CSS-COLOR-4]
    Tab Atkins Jr.; Chris Lilley. CSS Color Module Level 4. 5 July 2016. WD. URL: https://www.w3.org/TR/css-color-4/
    [CSS-DISPLAY-3]
    Elika Etemad. CSS Display Module Level 3. 20 July 2017. WD. URL: https://www.w3.org/TR/css-display-3/
    [CSS-GRID-1]
    Tab Atkins Jr.; Elika Etemad; Rossen Atanassov. CSS Grid Layout Module Level 1. 9 May 2017. CR. URL: https://www.w3.org/TR/css-grid-1/
    [CSS-INLINE-3]
    Dave Cramer; Elika Etemad; Steve Zilles. CSS Inline Layout Module Level 3. 24 May 2016. WD. URL: https://www.w3.org/TR/css-inline-3/
    [CSS-MASKING-1]
    Dirk Schulze; Brian Birtles; Tab Atkins Jr.. CSS Masking Module Level 1. 26 August 2014. CR. URL: https://www.w3.org/TR/css-masking-1/
    [CSS-POSITION-3]
    Rossen Atanassov; Arron Eicholz. CSS Positioned Layout Module Level 3. 17 May 2016. WD. URL: https://www.w3.org/TR/css-position-3/
    [CSS-SIZING-3]
    Elika Etemad. CSS Intrinsic & Extrinsic Sizing Module Level 3. 7 February 2017. WD. URL: https://www.w3.org/TR/css-sizing-3/
    [CSS-TRANSFORMS-1]
    Simon Fraser; et al. CSS Transforms Module Level 1. 26 November 2013. WD. URL: https://www.w3.org/TR/css-transforms-1/
    [CSS-TRANSFORMS-2]
    CSS Transforms Module Level 2 URL: https://drafts.csswg.org/css-transforms-2/
    [CSS-UI-4]
    Florian Rivoal. CSS Basic User Interface Module Level 4. 22 September 2015. WD. URL: https://www.w3.org/TR/css-ui-4/
    [CSS-VALUES-3]
    Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. 29 September 2016. CR. URL: https://www.w3.org/TR/css-values-3/
    [CSS22]
    Bert Bos. Cascading Style Sheets Level 2 Revision 2 (CSS 2.2) Specification. 12 April 2016. WD. URL: https://www.w3.org/TR/CSS22/
    [FILTER-EFFECTS-1]
    Dean Jackson; Erik Dahlström; Dirk Schulze. Filter Effects Module Level 1. 25 November 2014. WD. URL: https://www.w3.org/TR/filter-effects-1/
    [RFC2119]
    S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119

    Informative References

    [CSS-TEXT-3]
    Elika Etemad; Koji Ishii. CSS Text Module Level 3. 22 August 2017. WD. URL: https://www.w3.org/TR/css-text-3/

    Property Index

    Name Value Initial Applies to Inh. %ages Media Ani­mat­able Anim­ation type Canonical order Com­puted value
    border-collapse separate | collapse separate table-root boxes. yes n/a visual discrete per grammar as specified
    border-spacing <​length​>{1,2} 0px 0px table-root boxes when border-collapse is separate. yes n/a visual yes per grammar two absolute lengths
    caption-side top | bottom top table-caption boxes yes n/a visual discrete per grammar as specified
    empty-cells show | hide show table-cell boxes yes n/a visual discrete per grammar as specified
    table-layout auto | fixed auto table-root boxes. yes n/a visual discrete per grammar as specified

    Issues Index

    This is a breaking change from css 2.1 but matches implementations <https://github.com/w3c/csswg-drafts/issues/508>
    border-collapsing breaking change from 2.1 <https://github.com/w3c/csswg-drafts/issues/604>
    Change specificity in harmonization of collapsed borders? <https://github.com/w3c/csswg-drafts/issues/606>
    Handling of intrinsic offsets when in border collapsing mode <https://github.com/w3c/csswg-drafts/issues/608>
    EDITORIAL. The way this describes distribution of widths from colspanning cells is wrong. For min-content and max-content widths it should refer to the rules for distributing excess width to columns for intrinsic width calculation.
    Should min-width support percentages? <https://github.com/w3c/csswg-drafts/issues/607>
    EDITORIAL. Import the relevant section of §3.8.3 Computing Column Measures here.
    EDITORIAL. TODO. For current proposal, skip to §3.10.4 Distribution algorithm.
    We need a resolution on what visibility:collapse does. <https://github.com/w3c/csswg-drafts/issues/478>
    This only works in Firefox. It would make it easier to implement position:sticky in the future, though. [Chrome bug] [Interop risk: Firefox bug] <https://github.com/w3c/csswg-drafts/issues/858>
    Can we simplify empty-cells:hide? <https://github.com/w3c/csswg-drafts/issues/605>
    Should we hide the row-group background by saying cells only draw the backgrounds of visibility:visible grouping elements?