CSS Table Module Level 3

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:

• Its table-root element containing:
  • Zero, one or more table rows, optionally in row groups,
    • Each of them contaning one or more table cells
  • Optionally: one or more table columns, optionally in column groups
  • Optionally: one or more table caption.

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.

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-row-grouping box or element

A table-row-group, table-header-group, or table-footer-group box.

table-track box or element

A table-row, or table-column box.

table-track-grouping box or element

A table-row-grouping, or table-column-group box.

proper table child box or element

A table-track-grouping, table-track, or table-caption box.

proper table-row parent box or element

A table-root or a table-row-grouping box.

table-internal box or element

A table-cell, table-track or table-track-grouping 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.

slot

A slot is an available space created by the intersection of a row and a column in the table grid.

Define the table grid <https://github.com/w3c/csswg-drafts/issues/603>

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 element, a table-row element, and a table-cell element. Missing elements 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:
   1. Children of a table-column are treated as if they had display: none.
   2. Children of a table-column-group which are not a table-column are treated as if they had display: none.
   3. Anonymous inline boxes which contain only white space and are between two immediate siblings each of which is a table-non-root box, are treated as if they had display: none.
   4. Anonymous inline boxes which meet all of the following criteria are treated as though they had display: none.
      • contains only white space
      • are the first and/or last child of a tabular container
      • whose immediate sibling, if it has any siblings at all, is a table-non-root box
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-grouping 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 box, then an inline-table box must be generated; otherwise it must be a table box.
      • A table-row is misparented if its parent is neither a table-row-grouping nor a table-root box.
      • A table-column box is misparented if its parent is neither a table-column-group box nor a table-root box.
      • A table-row-grouping, table-column-group, or table-caption box is misparented if its parent is not a table-root 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.

2.2.2. Examples

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

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

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

<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; }

<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, if the table is empty:

   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.

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.

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.

<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>

<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>

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

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 only if it as an HTML element of the same type (otherwise, they act like they didnt’t have any attribute).

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. Change the spanning of the cells contained in those tracks accordingly so that no difference would be detectable in terms of slot assignment. (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 element its correct number of rows and columns (from its mapped element), and to each table-cell element its accurate table-row-start/table-column-start/table-row-span/table-column-span (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 cell in the row/column grid that is not occupied by an element or pseudo-element).

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

Beside their display type, those anonymous boxes do not receive any specific or default styling, except where otherwise mentioned by this specification (meaning their background is “transparent”, their padding is “0px” and their border is “none” by default).

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

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

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

3.5.2.1. The Border-Spacing property

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

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.

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.

• The computed values of properties position, float, margin-*, top, right, bottom, and left on the table box are used on the table-wrapper box and not the table box; the same holds true for the properties whose use could force the used value of transform-style to flat and their shorthands/longhands relatives: this list currently includes overflow, opacity, filter, clip, clip-path, isolation, mask-*, mix-blend-mode, transform-* and perspective.
  Where the table box values are not used on the table and/or table wrapper boxes, the unset values are used instead for that box (inherit or initial, depending on the property).
• The overflow property on the table-root and table-wrapper box, when its value is not either visible or hidden, is ignored and treated as if its value was visible.
• All css properties of table-column and table-column-group boxes are ignored, except when explicitly specified by this specification.
• The position of table-track and table-track-grouping boxes is ignored if its value is relative. User agents that support transform still need to support making these boxes containing blocks if required by spec.
• The margin, padding, overflow and z-index of table-track and table-track-grouping are ignored.
• The margin of table-cell boxes is ignored (as if it was set to 0px).
• The background of table-cell boxes are painted using a special background painting algorithm described in §4.3.2 Drawing cell backgrounds.

3.6.2. Overrides applying in collapsed-borders mode

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

• The padding of the table-root element is ignored (as if it was set to 0px).
• The border-spacing of the table-root element is ignored (as if it was set to 0px).
• The border-radius of both table-root and table-non-root boxes is ignored (as it it was set to 0px).
• The values used for the layout and rendering of the borders of the table-root element and the table-cell boxes it owns are determined using a special conflict resolution algorithm described in §3.7 Border-collapsing.

3.7. Border-collapsing

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

• Resolve conflicts with border-right:
  • Let C be an ordered set of table-cell element borders, sorted in Row/Column order of their parent cell; initially, let C contain only C°’s border-right
  • Add to the set C the border-left of all cells located after C° sharing a section of their border-left with C°’s border-right
  • Repeat the following two instructions, until no new cell is added to C:
    • For all newly-added cells C_i having a rowspan greater than one, add to the set C the border-right of all cells located before C_i sharing a section of their border-right with C_i’s border-left
    • For all newly-added cells C_i having a rowspan greater than one, add to the set C the border-left of all cells located after C_i sharing a section of their border-left with C_i’s border-right
  • Harmonize the conflicting borders of C
• Resolve conflicts with border-bottom:
  • Let C be an ordered set of table-cell element borders, sorted in Row/Column order of their parent cell; initially, let C contain only C°’s border-bottom
  • Add to the set C the border-top of all cells located after C° sharing a section of their border-top with C°’s border-bottom
  • Repeat the following two instructions, until no new cell is added to C:
    • For all newly-added cells C_i having a colspan greater than one, add to the set C the border-bottom of all cells located before C_i sharing a section of their border-bottom with C_i’s border-top
    • For all newly-added cells C_i having a colspan greater than one, add to the set C the border-top of all cells located after C_i sharing a section of their border-top with C_i’s border-bottom
  • Harmonize the conflicting borders of C
• 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 §4.3.3.1 Changes in collapsed-borders mode)

Then, for that table-root element:

• Harmonize the table-root element border-{top,bottom,left,right} with the corresponding border of all cells forming the border of the table (indenpendently), without actually modifying the border properties of the table-root element.
  
  If the table and the cell border styles have the same specificity, keep the cell border style.
  Once this is done, set the table-root element border-{…}-width to half the maximum width found during the harmonization processes for that border, then set border-{…}-style to solid, and border-{…}-color to transparent.

3.7.1.2. Harmonization Algorithm for Collapsed Borders

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

Given an ordered set of borders (BC_1, BC₂, … located in cells C_1, C₂, …) execute the following algorithm to determine the used value of the border properties for those conflicting borders.

• Set CurrentlyWinningBorderProperties to “border: 0px none transparent”
• For each border BC_i:
  • Consider the BC_i border’s properties
• If the border separates two columns:
  • For each border BC_i: Find the table-column element in which the C_i cell is located, if any. If the BC_i border is such that there is a border of the table-column element that would be drawn contiguously to it, consider its border’s properties.
  • For each border BC_i: Find the table-column-group element in which the C_i cell is located, if any. If the BC_i border is such that there is a border of the table-column-group element that would be drawn contiguously to it, consider its border’s properties.
• If the border separates two rows:
  • For each border BC_i: Find the table-row element in which the C_i cell is located, if any. If the BC_i border is such that there is a border of the table-row element that would be drawn contiguously to it, consider its border’s properties.
  • For each border BC_i: Find the table-row-group element in which the C_i cell is located, if any. If the BC_i border is such that there is a border of the table-row-group element that would be drawn contiguously to it, consider its border’s properties.
• Return CurrentlyWinningBorderProperties

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).

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:

• In separated-borders mode: the computed horizontal padding and border of the table-root
• In collapsed-borders mode: the used border-width values of the cell (half the winning border-width)

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

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 those defined above:

• The outer min-content width of a table cell is max(min-width, min-content width) adjusted by the cell intrinsic offsets.
• The outer min-content width of a table column or column group is max(min-width, width).
• The outer max-content width of a table cell in a non-constrained column is max(min-width, width, min-content width, min(max-width, max-content width)) adjusted by the cell intrinsic offsets.
• The outer max-content width of a table cell in a constrained column is max(min-width, width, min-content width, min(max-width, width)) adjusted by the cell intrinsic offsets.
• The outer max-content width of a table column or column group is max(min-width, min(max-width, width)).

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 terms for various parameters associated with each column of a table. These parameters are used in the following two subsections as part of the rules for computing intrinsic widths of tables and computing the column widths of a table.

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

intermediate min-content width for span 1

The largest of:

• the outer min-content width of the column group, if any
• the outer min-content width of the column, if any
• the outer min-content width of each cell in the column whose column-span is 1 (or just the one in the first row in fixed mode) or 0 if there is none

intermediate max-content width for span 1

The largest of:

• the outer max-content width of the column group, if any
• the outer max-content width of the column, if any
• the outer max-content width of each cell in the column whose column-span is 1 (or just the one in the first row if in fixed mode) or 0 if there is no such cell

intermediate intrinsic percentage width for span 1

The largest of the percentage contributions of each cell in the column whose column-span is 1, of the column (if any), and of the column group (if any)

intermediate min-content width for span N (N > 1)

the largest of the intermediate min-content width for span N-1 and the contributions of the cells in the column whose column-span is N, where the contribution of a cell is the result of taking the following steps:

1. Define the baseline (min-content / max-content) width as the sum of the intermediate (min-content / max-content) widths for span 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 for span N-1
   • the product of:
     • the ratio of:
       • the intermediate max-content width for span N-1 of the column minus the intermediate min-content width for span 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 intermediate max-content width for span 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

intermediate max-content width for span N (N > 1)

The largest of the intermediate max-content width for span N-1 and the contributions of the cells in the column whose column-span 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 intermediate max-content widths for span 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 for span N-1
   • the product of:
     • the ratio of the intermediate max-content width for span 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

intermediate intrinsic percentage width for span N (N > 1)

If the intermediate intrinsic percentage width for span N-1 is greater than 0%, then the intermediate intrinsic percentage width for span N is the same as the intermediate intrinsic percentage width for span N-1.

Otherwise, it is the largest of the contributions of the cells in the column whose column-span 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 intermediate intrinsic percentage width for span 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 intermediate intrinsic percentage width for span 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 intermediate intrinsic percentage width for span N-1 equal to zero.

min-content width

the intermediate min-content width for span N, where N is the number of columns in the table

max-content width

the intermediate max-content width for span N, where N is the number of columns in the table

intrinsic percentage width

the smaller of:

• intermediate intrinsic percentage width for span 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 (right) when direction is "ltr" ("rtl"))

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 non-column-spanning cells in the column has a computed width that is not "auto", and is not a percentage.

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:

• If the table-root element’s width property has a computed value (W) other than auto, the used width is the greater of W, CAPMIN, and GRIDMIN.
  If the used width is greater than GRIDMIN, the extra width should be distributed over the columns. See §3.9 Available Width Distribution.
• If the table-root element has 'width: auto', the used width is the greater of min(GRIDMAX, the table’s containing block width), CAPMIN, and GRIDMIN.

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.

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:

• percent-column:
  a column whose any constraint is defined to use a percentage only (with a value different from 0%)

• pixel-column:
  column whose any constraint is defined to use a defined length only (and is not a percent-column)

• auto-column:
  any other column

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

1. The min-content guess is the set of column width assignments where each column is assigned its min-content width.
2. The min-content-percentage 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 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 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.

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

Otherwise, the used widths of the columns are the result of starting from the max-content 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.

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:

• The minimum width of percent-columns and auto-columns is considered to be zero

• Cells ignore their border and padding size if their width is a percentage (box-sizing is ignored)

• If, when percentages are resolved based on the assignable table width, the sum of columns widths based on this resolution would exceed the assignable table width, they are instead to be resolved relative to their percentage value such that the sum of columns width meets the assignable table width exactly.

• Columns whose size is computed as a sum of a percentage and a pixel length must be sized as if they counted as two columns, one with the pixel value, the other with the percentage value.

3.9.3.2. Distributing excess width to columns

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

• for distributing the excess width of a table to its columns during the computation of the used widths of those columns (for used width calculation), or
• for distributing the excess max-content or min-content width of a column-spanning cell to the max-content or min-content widths of the columns it spans (for intrinsic width calculation).

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.

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 table-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, and will be distributed to the height of the table-rows.

The minimum height of a table-row is the maximum of:

• the row’s computed height (if definite, percentages being considered 0px)
• the computed height of each cell spanning the current row exclusively (if definite, percentages being treated as 0px), and
• the minimum height (ROWMIN) required by the cells spanning the row.

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).

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="https://w3.org/favicon.ico" /><p>Baseline</p></td>
  <td><img src="https://w3.org/favicon.ico" title="Baseline"/><br/><img src="https://w3.org/favicon.ico" title="After"/></td>
  <td><img src="https://w3.org/favicon.ico" /><img src="https://w3.org/favicon.ico" /></td>
</tr></table>

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.

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:

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 has no cell box aligned to its baseline, the baseline of that row is the bottom content edge of the lowest cell in the row.

Example showing how the previous algorithm creates the various alignment lines of a 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 for spans N>1, with the span=1 value being initialized with the largest of the resulting height of the previous row layout, and the largest specified height of cells that span this row only.

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

3.10.3. Core distribution principles

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

• its initial base height and
• its new base height (the one evaluated during the second layout pass, where percentages used in rowgroups/rows/cells' specified heights were resolved according to the table height, instead of being ignored as 0px).

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.

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

• width/height is:
  • the width/height assigned to the caption during layout
• top location is the sum of:
  • the height reserved for previous top captions (including margins), if any
  • any necessary extra top margin remaining after collapsing margins with the previous caption, if any.
• left location is the sum of:
  • the margin left of the caption
  • half of (the table width minus the width of caption and its total horizontal margin).

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

• width/height is the sum of:
  • the widths/heights of all spanned visible columns/rows
  • the horizontal/vertical border-spacing times the amount of spanned visible columns/rows minus one
• left/top location is the sum of:
  • for top: the height reserved for top captions (including margins), if any
  • the padding-left/padding-top and border-left-width/border-top-width of the table
  • the widths/heights of all previous visible columns/rows
  • the horizontal/vertical border-spacing times the amount of previous visible columns/rows plus one

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

• width/height is:
  • the width/height assigned to the caption during layout
• top location is the sum of:
  • the height reserved for top captions (including margins), if any
  • padding-top and border-top-width of the table
  • the height of all visible rows
  • padding-bottom and border-bottom-width of the table
  • the height reserved for previous bottom captions (including margins), if any
  • any necessary extra top margin remaining after collapsing margins with the previous bottom caption, if any.
• left location is the sum of:
  • the margin left of the caption
  • half of (the table width minus the width of caption and its total horizontal margin).

4. Rendering

4.1. 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.

4.2. Empty cell rendering (separated-borders mode)

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.

Cells are empty unless they contain one or more of the following:

• floating content, or
• in-flow content (other than white space that has been collapsed away by the white-space property handling).

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:

4.3. Drawing backgrounds and borders

4.3.1. Drawing table backgrounds and borders

Unlike other boxes types, table and inline-table boxes do not render their background and borders around their entire client rect. Indeed, the table captions are positioned between the table margins and its borders. Given backgrounds extends and original form the border-box area of an element (or one of the area contained inside the boder-box area like content-box), they are affected by this positioning scheme.

The padding of the table is accounted around the area occupied by the row/column grid Borders of the table box are rendered around the area occupied by the row/column grid and its padding. That area which contains the borders is the rectangular area which comprises of the full width of the table box, but does not contain the vertical areas occupied by the captions or their margins.

The border-box of the table is relative to the area described previously. The padding-box of the table is the rectangular area contained inside the border-box which does not interesct with the table borders (independently of whether the table draws them or not). The content-box of the table is the rectangular area contained inside the padding-box which does not interesct with the table paddings (this includes border-spacings at the edge of the table).

4.3.1.1. 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 §4.3 Drawing backgrounds and borders still apply if they are not overriden.

Borders of a table-root element are not laid out in collapsed-borders mode, except if the border-image property is set (or if the table has no cell).

In this 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 element.

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.

4.3.2. 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-grouping 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 on an element in one of the layers will only be visible if the layers above it have a transparent background.

0. The table background is being rendered by the table, and does not affect the cell background.
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.

4.3.3. Drawing cell borders

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

4.3.3.1. Changes in collapsed-borders mode

Borders of a table-cell element 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 §4.1 Paint order of cells and §3.7.1.1 Conflict Resolution Algorithm for Collapsed Borders.

4.3.4. 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. Fragmentation

5.1. 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.

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).

When break-before or break-after is applied to a table-row-grouping 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.

5.2. 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.

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.

6. Security Considerations

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

7. Privacy Considerations

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

8. List of bugs being tracked

This section is not normative.

• Align=center attribute overrides css margins in Edge
• Chrome applies nowrap quirks mode fix in DOCTYPE documents too
• Edge does not account for widths of spanned cells
• Chrome and Gecko do not apply display:table-cell on <button>
• Edge’s table-cell width unexplainably low due to percentage-max-width on content and colspan
• Table boxes should be wide enough to contain the caption
• Tables containing no row cannot have height in Chrome, but can in Edge/Firefox
• Table-layout:fixed causes different width distribution in Chrome
• Chrome distributes the height to each row differently then IE and firefox
• Height of rows which can overflow varies in Chrome vs Edge (percentage heights during min-height computation)
• Height specified on row groups is not interoperable
• Min-Height specified on rows is not interoperable
• Table with interleaved td[rowspan] rendered wrong in IE (145069)
• Row with explicit 'visibility:visible' lose background color when parent table has 'visibility: hidden'

9. Appendices

9.1. Mapping between CSS & HTML attributes

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

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 }

table {
  box-sizing: border-box;
  border-spacing: 2px;
  border-collapse: separate;
  text-indent: initial;
}

thead, tbody, tfoot, table > tr { vertical-align: middle; }
tr, td, th { vertical-align: inherit; }

td, th { padding: 1px; }
th { font-weight: bold;  }

table, td, th { border-color: gray; }
thead, tbody, tfoot, tr { border-color: inherit; }



table[frame=box i], table[frame=border i], table[frame=hsides i], table[frame=above i], table[frame=below i], table[frame=vsides i], table[frame=lhs i], table[frame=rhs i] {
  border: 1px solid inset;
}


table:matches([rules=all i], [rules=rows i], [rules=cols i], [rules=groups i], [rules=none i]) {
  border-collapse: collapse;
  border-style: hidden;
}

table:matches([rules=all i], [rules=rows i], [rules=cols i], [rules=groups i], [rules=none i]),
table:matches([rules=all i], [rules=rows i], [rules=cols i], [rules=groups i], [rules=none i]) > :matches(thead,tbody,tfoot) > tr > :matches(th,td) {
  border-color: black;
}

table[border=$border] /* if(parseInt($border) > 0) */ {
  border: /*(parseInt($border) * 1px)*/ outset rgb(128, 128, 128);
}
table[border=$border] > :matches(thead,tbody,tfoot) > tr > :matches(th,td) /* if(parseInt($border) > 0) */ {
  border: 1px inset rgb(128, 128, 128);
}

table[rules=all i] > :matches(thead,tbody,tfoot) > tr > :matches(th,td) {
  border: 1px solid grey;
}
table[rules=rows i] > :matches(thead,tbody,tfoot) > tr > :matches(th,td) {
  border: 1px solid grey;
  border-left: none;
  border-right: none;
}
table[rules=cols i] > :matches(thead,tbody,tfoot) > tr > :matches(th,td) {
  border: 1px solid grey;
  border-top: none;
  border-bottom: none;
}
table[rules=none i] > :matches(thead,tbody,tfoot) > tr > :matches(th,td) {
  border: none;
}

table[rules=groups i] > :matches(thead,tbody,tfoot) {
  border-top-width: 1px; border-top-style: solid;
  border-bottom-width: 1px; border-bottom-style: solid;
}
table[rules=groups i] > colgroup {
  border-left-width: 1px; border-left-style: solid;
  border-right-width: 1px; border-right-style: solid;
}

table[frame=box i], table[frame=border i], table[frame=hsides i], table[frame=above i], table[frame=below i], table[frame=vsides i], table[frame=lhs i], table[frame=rhs i] {
  border-style: outset;
}
table[frame=below i], table[frame=vsides i], table[frame=lhs i], table[frame=rhs i] {
  border-top-style: hidden;
}
table[frame=above i], table[frame=vsides i], table[frame=lhs i], table[frame=rhs i] {
  border-bottom-style: hidden;
}
table[frame=hsides i], table[frame=above i], table[frame=below i], table[frame=rhs i] {
  border-left-style: hidden;
}
table[frame=hsides i], table[frame=above i], table[frame=below i], table[frame=rhs i] {
  border-right-style: hidden;
}

table[cellpadding=$x] > :matches(thead,tbody,tfoot) > tr > :matches(th,td) /* if(parseInt($x)>0) */ {
  padding: /*(parseInt($x) * 1px)*/;
}
table[cellspacing=$x] /* if(parseInt($x)>0) */ {
  border-spacing: /*(parseInt($x) * 1px)*/;
}


table[width=$w] /* if(parseInt($w) > 0) */ {
  width: /*(parseInt($w) * 1px)*/;
}
table[width=$w] /* if($w matches /(+|-|)([0-9]+([.][0-9]+|)|([.][0-9]+))[%]/) */ {
  width: /*(parseInt($w) * 1px)*/;
}
table[height=$h] /* if(parseInt($h) > 0) {
  height: /*(parseInt($h) * 1px)*/;
}
table[height=$h] /* if($h matches /(+|-|)([0-9]+([.][0-9]+|)|([.][0-9]+))[%]/) */ {
  height: /*(parseInt($h) * 1px)*/;
}


table[bordercolor=$color] {
  border-color: /*parseHTMLColor($color)*/;
}
table[bordercolor] > :matches(tbody, thead, tfoot, tr, colgroup, col),
table[bordercolor] > :matches(tbody, thead, tfoot) > tr,
table[bordercolor] > :matches(tbody, thead, tfoot) > tr > :matches(td, th),
table[bordercolor] > tr > :matches(td, th)
table[bordercolor] > colgroup > col
) {
  border-color: inherit;
}
table[bgcolor=$color] {
  background-color: /*parseHTMLColor($color)*/;
}
table[align=left i] {
  float: left;
}
table[align=right i] {
  float: right;
}
table[align=center i] {
  margin-left: auto;
  margin-right: auto;
}

caption[align=bottom i] { caption-side: bottom; }
:matches(thead,tbody,tfoot,tr,td,th)[valign=top i] {
  vertical-align: top;
}
:matches(thead,tbody,tfoot,tr,td,th)[valign=middle i] {
  vertical-align: middle;
}
:matches(thead,tbody,tfoot,tr,td,th)[valign=bottom i] {
  vertical-align: bottom;
}
:matches(thead,tbody,tfoot,tr,td,th)[valign=baseline i] {
  vertical-align: baseline;
}

:matches(thead,tbody,tfoot,tr,td,th)[align=absmiddle i] {
  text-align: center;
}

:matches(colgroup,col,thead,tbody,tfoot,tr,td,th)[hidden] {
  visibility: collapse;
}

:matches(td,th)[nowrap] { white-space: nowrap; }
:matches(td,th)[nowrap][width=$w] /* if(quirksMode && parseInt($w) > 0) */ {
  white-space: normal;
}

10. (link here for missing sections)