csswg-drafts/css3-tables/Overview.src.html at bcfe3ccaf2eda72e18054edea7af739b34745c6f · w3c/csswg-drafts · GitHub

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
  <title>CSS3 Tables Module</title>
  <link rel="stylesheet" type="text/css" href="../default.css">
  <style type="text/css">
  /* Just in case an incorrect max-width occurs in default.css */
  body {max-width: none !important}
  </style>
  <link rel="stylesheet" type="text/css"
  href="http://www.w3.org/StyleSheets/TR/W3C-MO">
</head>

<body>

<div class="head">
<!--logo-->

<h1>CSS3 Tables Module</h1>

<h2 class="no-num no-toc">[LONGSTATUS] [DATE: 21 Feb 2002]</h2>
<dl>
  <dt>This version:</dt>
    <dd><a
      href="[VERSION]">http://www.w3.org/[YEAR]/MO-css3-tables-[CDATE]</a></dd>
  <dt>Latest version:</dt>
    <dd><a
      href="[LATEST]">[LATEST]</a></dd>
  <dt>Previous version:</dt>
    <dd><a
      href="[http://www.w3.org/PreviousVersionURI]">[http://www.w3.org/PreviousVersionURI]</a></dd>
  <dt>Feedback:</dt>
    <dd><a href="mailto:www-style@w3.org?subject=%5B[css-tables]%5D%20feedback">www-style@w3.org</a>
        with subject line &ldquo;<kbd>[css-tables] <var>&hellip; message topic &hellip;</var></kbd>&rdquo;
        (<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/">archives</a>)
  <dt>Editors:</dt>
    <dd><a href="http://www.w3.org/People/Bos">Bert Bos</a>, <a
      href="http://www.w3.org/">W3C</a>, <a
      href="mailto:bert@w3.org">&lt;bert@w3.org&gt;</a></dd>
    <dd>[editor name, affiliation (opt.), email address (opt.)]</dd>
</dl>

<!--copyright-->

<hr title="Separator for header">
</div>


<h2 id=abstract class="no-num no-toc">Abstract</h2>

<p>CSS (Cascading Style Sheets) is a language for specifying the
rendering of a structured document (in HTML or XML). See the CSS3
introduction [[CSS3INTRO]] for more on CSS. The <em>CSS3 table
module</em> is one of the modules of level 3 of CSS and defines the
properties that specify how tables are to be displayed visually or
spoken by a speech synthesizer.

<p>This is a very rough draft. It consists of the text of
the CSS2 chapter on tables, with almost no changes yet., except for
the addition of the first section, "Tabs &amp; leaders."

<h2 id=status class="no-num no-toc">Status of this document</h2>

<p style="background: #fdd; color: red; font-weight: bold; text-align: center; padding: .5em; border: thick solid red; border-radius: 1em">This specification is not being actively maintained, and should not be used as a guide for implementations.  It may be revived in the future, but for now should be considered obsolete.  <br>If you have questions or comments on this specification, please send an email to the CSS Working Group's mailing list at <a href="mailto:www-style@w3.org">www-style@w3.org</a>.  (Before sending mail for the first time, you have to subscribe at <a href="http://lists.w3.org/Archives/Public/www-style/">http://lists.w3.org/Archives/Public/www-style/</a>.)</p>

<!--status-->

<p>The text hasn't yet been synchronized with the latest version of
CSS 2.1.

<h2 class="no-num no-toc"><a name="contents">Table of contents</a></h2>

<!--toc-->

<hr>

<h2>Dependencies on other modules</h2>

<p>This CSS3 module depends on the following other CSS3 modules:
<ul>
  <li>CSS3 Box Model [[!CSS3BOX]]
  <li>CSS3 Syntax Module [[!CSS3SYN]]
  <li>CSS3 Values and Units Module [[!CSS3VAL]]
  <li>[module]
</ul>

<h2>The 'tab' properties: tabs and leaders</h2>

<p class="issue">[Does it belong here, or in the line box model?]

<p class="issue">[This material is new. (Well, actually, <a
href="css-tabs.html">it dates from 1996</a>, but it is new in this
draft.) Not reviewed yet in any way.]

<p class="issue">[The name "tab" maybe reminds people too much of the tab
character, which plays no role here at all. Maybe a different name is better.
"Anchor"?]

<p class="issue">[Could this be merged with the margin-left/margin-right
properties to save some properties? 'margin-left: 25% fixed' instead of 'tab:
25% left'?]

<p class=issue>Håkon will write a proposal for a
'leader(&lt;string&gt;)' notation that can be put in the 'content'
property, inside '::after' and '::before', independent of any tab
properties. It will push everything after it (up to the end of the
block or the explicit next line break, whichever comes first) forward,
so that it ends at the end of a line. Often, that may make tabs
unnecessary. [12 Jan 2005] That proposal is now in [[CSS3GCPM]].

<table class="propdef">
  <tbody>
    <tr>
      <td><em>Name:</em>
      <td><dfn>tab-position</dfn>

    <tr>
      <td><em>Value:</em>
      <td><var>&lt;length&gt;</var> | <var>&lt;percentage&gt;</var>

    <tr>
      <td><em>Initial:</em>
      <td>0

    <tr>
      <td><em>Applies to:</em>
      <td>inline-level elements

    <tr>
      <td><em>Inherited:</em>
      <td>no

    <tr>
      <td><em>Percentages:</em>
      <td>width* of containing block

    <tr>
      <td><em>Media:</em>
      <td>visual

    <tr>
      <td><em>Computed&nbsp;value:</em>
      <td>&lt;length&gt;

    <tr>
      <td colspan="2">*) if the containing block is 'horizontal', otherwise
        height


</table>

<table class="propdef">
  <tbody>
    <tr>
      <td><em>Name:</em>
      <td><dfn>tab-align</dfn>

    <tr>
      <td><em>Value:</em>
      <td>left | top | center | right | bottom | <var>&lt;string&gt;</var> |
        none

    <tr>
      <td><em>Initial:</em>
      <td>none

    <tr>
      <td><em>Applies to:</em>
      <td>inline-level elements

    <tr>
      <td><em>Inherited:</em>
      <td>no

    <tr>
      <td><em>Percentages:</em>
      <td>N/A

    <tr>
      <td><em>Media:</em>
      <td>visual

    <tr>
      <td><em>Computed&nbsp;value:</em>
      <td>specified value


</table>

<table class="propdef">
  <tbody>
    <tr>
      <td><em>Name:</em>
      <td><dfn>tab-leaders</dfn>

    <tr>
      <td><em>Value:</em>
      <td><var>&lt;string&gt;</var>

    <tr>
      <td><em>Initial:</em>
      <td>"" (empty string)

    <tr>
      <td><em>Applies to:</em>
      <td>inline-level elements

    <tr>
      <td><em>Inherited:</em>
      <td>no

    <tr>
      <td><em>Percentages:</em>
      <td>N/A

    <tr>
      <td><em>Media:</em>
      <td>visual

    <tr>
      <td><em>Computed&nbsp;value:</em>
      <td>specified value


</table>

<table class="propdef">
  <tbody>
    <tr>
      <td><em>Name:</em>
      <td><dfn>tab-leaders-alignment</dfn>

    <tr>
      <td><em>Value:</em>
      <td>aligned | centered | distributed

    <tr>
      <td><em>Initial:</em>
      <td>aligned

    <tr>
      <td><em>Applies to:</em>
      <td>inline-level elements

    <tr>
      <td><em>Inherited:</em>
      <td>no

    <tr>
      <td><em>Percentages:</em>
      <td>N/A

    <tr>
      <td>visual

    <tr>
      <td><em>Computed&nbsp;value:</em>
      <td>specified value


</table>

<table class="propdef">
  <tbody>
    <tr>
      <td><em>Name:</em>
      <td><dfn>tab</dfn>

    <tr>
      <td><em>Value:</em>
      <td>[ &lt;'tab-position'&gt; || &lt;'tab-align'&gt; ] [ / [
        &lt;'tab-leaders'&gt; || &lt;'tab-leaders-alignment'&gt; ] ]?

    <tr>
      <td><em>Initial:</em>
      <td>see individual properties

    <tr>
      <td>inline-level elements

    <tr>
      <td><em>Inherited:</em>
      <td>no

    <tr>
      <td><em>Percentages:</em>
      <td>see individual properties

    <tr>
      <td><em>Media:</em>
      <td>visual

    <tr>
      <td><em>Computed&nbsp;value:</em>
      <td>see individual properties


</table>

<p>An inline element can be put at a specific position in the line by setting
the element's <span class="property">'tab'</span> property. The space that
creates before the element can be filled with <dfn>leaders</dfn> or left
blank.

<div class="example">
<p>Here are some examples:
<pre>signature { tab: 100% right }      /* right-aligned at end of line */
amount { tab: -1em "." }           /* aligned on dot, 1em from end of line */
desc { tab: 0 left }               /* left-aligned to start of line */
pageno { tab: 100% right / " . " } /* right-aligned, with dot leaders */
col2 { tab: 50% center / " · " }   /* centered in the line */</pre>

<p>With a document fragment like the following:
<pre>&lt;expenses&gt;
&lt;desc&gt;Hotel&lt;/desc&gt; &lt;amount&gt;374.55&lt;/amount&gt;
&lt;desc&gt;Travel&lt;/desc&gt; &lt;amount&gt;1460.10&lt;/amount&gt;
&lt;desc&gt;Miscellaneous, including presents and
tips&lt;/desc&gt; &lt;amount&gt;84.00&lt;/amount&gt;
&lt;desc&gt;Total&lt;/desc&gt; &lt;amount&gt;1918.65&lt;/amount&gt;
&lt;signature&gt;Ph. Fogg&lt;/signature&gt;
&lt;/expenses&gt;</pre>

<p>The rendering might be as follows:

<div class="figure">
<p><img src="tabs.png" alt="[image]">

<p class="caption">Possible rendering of a text with tabs and leaders
</div>
</div>

<p>The <span class="property">'tab-position'</span> and <span
class="property">'tab-align'</span> determine the position of the element in
the line. The element is positioned by inserting extra whitespace or leaders
before it. Setting a tab will never cause the element to overlap any other
element on the line (unless it would already overlap without the tab, because
of negative margins). It may be necessary for the UA to insert so much
whitespace/leaders, that the alignment point of the tab occurs on one of the
following lines. (The example above shows one such case.)

<p>The <span class="property">'tab-position'</span> gives the position of a
point on the line to which the element will be aligned. A negative
<var>&lt;length&gt;</var> is measured from the end of the line, a nonnegative
one from the beginning. Ditto for percentages, where percentages are relative
to the width of the <span>containing block</span> (or height, if the
containing block's <span>orientation</span> is vertical). It depends on the
writing mode of the containing block which edge is the start of the line.
<span class="issue">[Or is it more intuitive to always count positive lengths
from the left or top and negative ones from the right or bottom?]</span>

<p>The position is measured from the <em>content edge</em> of the containing
block and is independent of any floats that may make the line box narrower
than the content box. As usual for inline elements in the presence of floats,
the alignment point and the element to which it belongs will be moved to a
following line, if it would otherwise overlap the float.

<p class="note">Note that a value of '0' means the start of the line. Use
100% to refer to the end of the line.

<p><span class="property">'Tab-align'</span> specifies how the element is
aligned to the alignment point:
<dl>
  <dt>'none'</dt>
    <dd>The element is not aligned to any alignment point and is put
      immediately after the previous element, with no intervening
    leaders.</dd>
  <dt>'left', 'top'</dt>
    <dd>These are the same and mean that the left <em>margin edge</em> (or
      top, if vertical) of the element is at the given position in the line.
      <p>If the element consists of multiple boxes (because of bidi
      processing or line breaks), which of the boxes is aligned depends on
      the <span class="property">'direction'</span> of the containing block:
      the first box in the case of <span class="css">'ltr'</span>, the last
      box in the case of <span class="css">'rtl'</span>.
    </dd>
  <dt>'right', 'bottom'</dt>
    <dd>The right <em>margin edge</em> (or bottom, if vertical) is at the
      given position. If the <span class="property">'direction'</span> of the
      containing block is <span class="css">'ltr'</span>, the element's last
      box is aligned, otherwise the first box.</dd>
  <dt>'center'</dt>
    <dd>The element is centered around the given position. If a line break
      occurs inside the element, the element might not be centered
    exactly.</dd>
  <dt><var>&lt;string&gt;</var></dt>
    <dd>The beginning of the first occurrence of the string in the element is
      put at the alignment point. If the string does not occur in the
      element, the end of the content of the element is aligned.</dd>
</dl>

<p class="issue">[Do we need 'start' and 'end' keywords that dynamically
resolve to 'left' or 'right' depending on the writing direction? Probably not
very useful. Ltr and rtl are not symmetrical: even in rtl text, numbers are
right aligned.]

<p>The <span class="property">'tab-leaders'</span> property determines what
is inserted before the element to make it align. If the value is the empty
string, only whitespace is inserted, otherwise multiple copies of the string
are inserted, as many as needed. If there is not room for a whole number of
copies, the remaining part is filled with whitespace. The style (color, font,
etc.) of the leaders is that of the element's parent (i.e., not necessarily
the same as the element's own style).

<p>The values of <span class="property">'tab-leaders-alignment'</span> have
the following meaning:
<dl>
  <dt>'centered'</dt>
    <dd>If the space for the leaders is not a whole number of copies of the
      <span class="property">'tab-leaders'</span> string, half of the extra
      whitespace is inserted before the first string, and half after the last
      string. (If there is a line break the middle of the leaders, it may not
      be possible to have exactly half the space on both sides.)</dd>
  <dt>'distributed'</dt>
    <dd>Like for <span class="css">'centered'</span>, but the extra
      whitespace is inserted in equal amounts before the first, after the
      last and between the strings.</dd>
  <dt>'aligned'</dt>
    <dd>The <span class="property">'tab-leaders'</span> strings are
      positioned such that there is room for exactly a whole number of copies
      between the string and the left content edge of the containing block.
      <span class="note">Note that this has the effect that all 'aligned'
      leaders on different lines are aligned with each other, as if they were
      attached to a common grid. The dot leaders in the previous example form
      such a grid.</span></dd>
</dl>

<p>The <span class="property">'tab'</span> property is a shorthand to set all
four properties together. Omitted values default to their initial values.

<p class="note">Note the slash (/) in the value of <span
class="property">'tab'</span>: if leaders are specified, they must be
separated from the position &amp; alignment with a slash.

<p class="note">Note that <span class="css">'tab: 2em / "."'</span> is a
valid, and occasionally useful declaration, but by itself does not cause any
leaders to appear, because it implicitly sets <span
class="property">'tab-align'</span> to <span class="css">'none'</span>.

<p>Justification and line breaking algorithms may change the size of an
element, but leave it aligned at the alignment point. (Although different
algorithms and different settings of the relevant properties may cause the
alignment point to fall on different lines.)

<p class="issue">[Do we need keywords such as 'arrow-leader (for a stretchy
arrow) or 'double-arrow-leader', or can they be made from existing
characters? Or should 'tab-leaders' accept up to 3 strings, e.g., "\2190"
"\2500" "\2192" ("&#x2190;" "&#x2500;" "&#x2192;"), for start, middle and end
of the leaders?]

<h2>Introduction to tables</h2>

<p class=issue>What happens with tables in vertical text
('writing-mode: tb-rl' etc.)? Are tables rotated or not? Currently,
the specification says rows are horizontal and the only influence is
from 'direction', which may cause the next column to be on the left of
the current one instead of the right.

<p>Table mark-up in a source document typically represents a
particular relationship between three or more dimensions of data,
e.g., dates, products and the number of units sold. Table properties
in CSS are meant to style the representation of such data as a table.
But the properties can occasionally also be used to align elements in
rows and columns for purely visual reasons, rather than semantics.
Unlike, e.g., the <code class=html>table</code> element in HTML, the
<span class=property>'table'</span> keyword doesn't imply any
particular semantic relation between elements in the document.

<div class=example><p>
Here is a simple three-row, three-column
table described in HTML&nbsp;4:

<pre class="html-example">
&lt;TABLE&gt;
&lt;CAPTION&gt;This is a simple 3x3 table&lt;/CAPTION&gt;
&lt;TR id="row1"&gt;
   &lt;TH&gt;Header 1  &lt;TD&gt;Cell 1  &lt;TD&gt;Cell 2
&lt;TR id="row2"&gt;
   &lt;TH&gt;Header 2  &lt;TD&gt;Cell 3  &lt;TD&gt;Cell 4
&lt;TR id="row3"&gt;
   &lt;TH&gt;Header 3  &lt;TD&gt;Cell 5  &lt;TD&gt;Cell 6
&lt;/TABLE&gt;
</pre>

<p>This code creates one table (the <code class=html>TABLE</code>
element), three rows (the <code class=html>TR</code> elements), three
header cells (the <code class=html>TH</code> elements), and six data
cells (the <code class=html>TD</code> elements). Note that the three
columns of this example are specified implicitly: there are as many
columns in the table as required by header and data cells.

<p>The following CSS rule centers the text horizontally in the header
cells and presents the text in the header cells with a bold font
weight:

<pre>
th { text-align: center; font-weight: bold }
</pre>

<p>The next rules align the text of the header cells on their baseline
and vertically center the text in each data cell:

th { vertical-align: baseline }
td { vertical-align: middle }
</pre>

<p>The next rules specify that the top row will be surrounded by a 3px
solid blue border and each of the other rows will be surrounded by a
1px solid black border:

<pre>
table   { border-collapse: collapse }
tr#row1 { border: 3px solid blue }
tr#row2 { border: 1px solid black }
tr#row3 { border: 1px solid black }
</pre>

<p>Note, however, that the borders around the rows overlap where the
rows meet. What color (black or blue) and thickness (1px or 3px) will
the border between row1 and row2 be? We discuss this in the section on
<a href="#border-conflict-resolution">border conflict resolution.</a>

<p>The following rule puts the table caption above the table:

<pre>
caption { caption-side: top }
</pre>

</div>

<p>The preceding example shows how CSS works with HTML 4 elements;
in HTML 4, the semantics of the various table elements (TABLE,
CAPTION, THEAD, TBODY, TFOOT, COL, COLGROUP, TH, and TD) are
well-defined. In other document languages (such as XML applications),
there may not be pre-defined table elements. Therefore, CSS&nbsp;2.1 allows
authors to <span class="index-inst" title="mapping elements to table
parts">"map"</span> document language elements to table elements via
the <span class="propinst-display">'display'</span> property. For
example, the following rule makes the FOO element act like an HTML
TABLE element and the BAR element act like a CAPTION element:</p>

<PRE class="example">
FOO { display : table }
BAR { display : table-caption }
</pre>

<p id=internal>We discuss the various table elements in the
following section. In
this specification, the term <span class="index-def" title="table
element"><dfn>table element</dfn></span> refers to any element
involved in the creation of a table. An <span class="index-def"
title="internal table element|table
element::internal">“internal”
table element</span> is one that produces a row, row group, column,
column group, or cell.

<h2>The CSS table model</h2>

<p>The CSS table model is based on the HTML&nbsp;4.0 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. The table model is said to be “row
primary,&#8221 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 each row belongs to the first column,
the second to the second column, etc.). Rows and columns may be
grouped structurally and this grouping reflected in presentation
(e.g., a border may be drawn around a group of rows).

<p>Thus, the table model consists of tables, captions, rows, row
groups, columns, column groups, and cells.

<p>The CSS model does not require that the <span>document
language</span> 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:

<dl>
  <dt><dfn>table</dfn> (In HTML: TABLE) <dd>Specifies that an element
  defines a <em>block-level</em> table: it is a rectangular block that
  participates in a <em>block formatting context</em>.

  <dt><dfn>inline-table</dfn> (In HTML: TABLE) <dd>Specifies that an
  element defines an <em>inline-level</em> table: it is a rectangular
  block that participates in an <em>inline formatting context</em>.

  <dt><dfn>table-row</dfn> (In HTML:
  TR) <dd>Specifies that an element is a row of cells.

  <dt><dfn>table-row-group</dfn>
  (In HTML: TBODY) <dd>Specifies that an element groups one or more
  rows.

  <dt><dfn>table-header-group</dfn>
  (In HTML: THEAD) <dd>Like 'table-row-group', but for visual
  formatting, the row group is always displayed before all other rows
  and row groups and after any top captions. Print user agents may
  repeat header rows on each page spanned by a table. If a table
  contains multiple elements with 'display: table-header-group', only
  the first is rendered as a header; the others are treated as if they
  had 'display: table-row-group'.

  <dt><dfn>table-footer-group</dfn>
  (In HTML: TFOOT) <dd>Like 'table-row-group', but for visual
  formatting, the row group is always displayed after all other rows
  and row groups and before any bottom captions. Print user agents may
  repeat footer rows on each page spanned by a table. If a table
  contains multiple elements with 'display: table-footer-group', only
  the first is rendered as a footer; the others are treated as if they
  had 'display: table-row-group'.

  <dt><dfn>table-column</dfn> (In
  HTML: COL) <dd>Specifies that an element describes a column of
  cells.

  <dt><dfn>table-column-group</dfn>
  (In HTML: COLGROUP) <dd>Specifies that an element groups one or more
  columns.

  <dt><dfn>table-cell</dfn> (In HTML:
  TD, TH) <dd>Specifies that an element represents a table cell.

  <dt><dfn>table-caption</dfn> (In
  HTML: CAPTION) <dd>Specifies a caption for the table. All elements
  with 'display: table-caption' must be rendered, as described in
  <a href="#model">section [??].</a>
</dl>

<p>Replaced elements with these
'display' values are treated as their
given display types during layout. For example, an image that is set
to 'display: table-cell' will fill the available cell space, and its
dimensions might contribute towards the table sizing algorithms, as
with an ordinary cell.

<p>Elements with 'display' set
to 'table-column' or 'table-column-group' are not rendered (exactly as
if they had 'display: none'), but they are useful, because they may
have attributes which induce a certain style for the columns they
represent.

<div class=issue>
<p>The above, rewritten for 'display-model' and 'display-role':

<p>The values of <span class=property>'display-model'</span> that
apply to tables have the following meaning. (For the purposes of the
definitions in this section, any child elements with a <span
class=property>'display-role'</span> of <span class=css>'none'</span>
are considered to have been removed from the document tree.)

<dl>
  <dt>table
  <dd>
    <p>The child elements are laid out as a stack of row-groups. In
    detail:

    <p>Any uninterrupted sequence of child elements, including
    anonymous ones, with a role other than <span
    class=css>'table-{row,header,footer}-group'</span> or <span
    class=css>'table-caption'</span> is wrapped in an anonymous
    element with role and model both set to <span
    class=css>'table-row-group'</span>.

    <p>The resulting set of children is laid out as a stack of rows
    from top to bottom, with at the top any <span
    class=css>'table-header-group'</span> child, then the <span
    class=css>'table-row-group'</span> children, in the order of the
    document, and finally any <span
    class=css>'table-footer-group'</span> child. (Note also the
    difference between these three types for paged media, described <a
    href="#table-header-group">below.</a>)

  <dt>table-row-group
  <dd>
    <p>The children are laid out as a stack of rows. In detail:

    <p>Any uninterrupted sequence of child elements with a role other
    than <span class=css>'table-row'</span> is wrapped in an anonymous
    element with role set to <span class=css>'table-row'</span> and
    model set to <span class=css>'block-inside'</span>.

    <p>The resulting children are laid out as a stack of rows from top
    to bottom in the order of the document.

  <dt>table-row
  <dd>
    <p>The children are laid out as a row of table cells. In detail:

    <p>Any uninterrupted sequence of children with a role other than
    <span class=css>'table-cell'</span> is wrapped in an anonymous
    element with role set to <span class=css>'table-cell'</span> and
    model set to <span class=css>'block'</span>.

    <p>The resulting children are laid out from left to right in the
    order of the document.

  <dt>table-column-group
  <dd>
    <p>Any children with a role other than <span
    class=css>'table-column'</span> are ignored. The other children
    aren't rendered either, but some of their properties influence the
    style of the table. See the section <a
    href="#columns">Columns</a> below.

  <dt>table-column
  <dd>
    <p>All children are ignored (as if their <span
    class=property>'display-role'</span> was <span class=css>'none'</span>)
    See the section <a href="#columns">Columns</a> below for the
    function of properties on this element.
</dl>

<p>See <a href="#width-layout">Table width algorithms</a> and <a
href="#height-layout">Table height algorithms</a> for the size of the
various elements.

<p>Where it says “top to bottom” or “left to
right” in the definitions above, this should be replaced by the
appropriate direction based on the value of <span
class=property>'writing-mode'</span> of the enclosing <span
class=css>'table'</span> element, as follows. (Note that the writing
mode of other elements in the table may influence the direction of the
context of the table cells, but only the writing mode of the table
element itself determines the direction of the rows and columns.)

<dl>
  <dt>lr-tb <dd>Rows are stacked top to bottom and columns are laid
  out from left to right (i.e., as in the definitions above).

  <dt>rl-tb <dd>Rows are stacked top to bottom and columns are laid
  out right to left.

  <dt>tb-rl <dd>Rows are laid out from right to left and columns from
  top to bottom.

  <dt>tb-lr <dd>Rows are laid out from left to right and columns from
  top to bottom.
</dl>

<p class=note>Note that there are theoretically 8 ways that rows and
columns can be ordered, but only the above 4 are supported.

<p>The values of <span class=property>'table-role'</span> have the
following meaning

<dl>
  <dt>table-cell
  <dd>
    <p>The element is a cell in a table row. If the parent, anonymous
    or not, doesn't have the model <span class=css>'table-row'</span>,
    an anonymous element is wrapped around this element and all its
    sister elements with the same role that form an uninterupted
    sequence. The anonymous element has a role and a model of <span
    class=css>'table-row'</span>.

  <dt>table-caption
  <dd>
    <p>The element is the caption of a table. If the parent, anonymous
    or not, has a model other than <span class=css>'table'</span>, an
    anonymous element is wrapped around this element and any sisters
    with a role of 'table-{row,header,footer}-group', 'table-row',
    'table-column-group' or 'table-column' that form an uninterrupted
    sequence. The anonymous element has a role of <span
    class=css>'block'</span> and a model of <span
    class=css>'table'</span>.

    <p>If the <span class=css>'table'</span> element that is this
    element's parent has another child with role <span
    class=css>'table-caption'</span> earlier in the document, this
    element is treated as if it had a role of <span
    class=css>'block'</span> instead. <span class=issue>[In
    CSS&nbsp;2.1 we said this situation was undefined and authors
    should not use it...]</span>
  <dt>table-row-group
  <dd>
    <p>The element is a group of rows. If the parent, anonymous or
    not, has a model other than <span class=css>'table'</span>, an
    anonymous element is wrapped around this element and all its
    sister elements with a role of <span
    class=css>table-{row,header,footer}-group'</span> that form an
    uninterupted sequence. The anonymous element has a role of <span
    class=css>'block'</span> and a model of <span
    class=css>'table'</span>.

  <dt id="table-header-group">table-header-group
  <dd>
    <p>The element is a group of rows that is displayed at the top of
    the table, after any top caption. In paged media, if a page break
    occurs in the table, the header group is repeated at the top of
    the table after every page break.

    <p>If the parent, anonymous or not, has a model other than <span
    class=css>'table'</span>, an anonymous element is wrapped around
    this element and all its sister elements with a role of <span
    class=css>table-{row,header,footer}-group'</span> that form an
    uninterupted sequence. The anonymous element has a role of <span
    class=css>'block'</span> and a model of <span
    class=css>'table'</span>.

  <dt>table-footer-group
  <dd>
    <p>The element is a group of rows that is displayed at the bottom
    of the table, before any bottom caption. In paged media, if a page
    break occurs in the table, the footer group is repeated at the
    bottom of the table before every page break.

    <p>If the parent, anonymous or not, has a model other than <span
    class=css>'table'</span>, an anonymous element is wrapped around
    this element and all its sister elements with a role of <span
    class=css>table-{row,header,footer}-group'</span> that form an
    uninterupted sequence. The anonymous element has a role of <span
    class=css>'block'</span> and a model of <span
    class=css>'table'</span>.

  <dt>table-column
  <dd>
    <p>The element creates a column. It's contents are ignored.

    <p>If the parent, anonymous or not, has neither the model <span
    class=css>'table'</span> nor <span
    class=css>'table-column-group'</span>, an anonymous element is
wrapped around this element and any sisters with a role of
<dd>

</dl>
</div>

<p class="issue">An <a
href="http://lists.w3.org/Archives/Public/www-style/2002Mar/0023.html">
idea</a> by Dorothea Salo of Open eBook Forum: some way to scroll a
table and keep the headers and footers on screen, plus a a vertical
analogue. Such "header columns" would stay on the screen during
horizontal scrolling.

<div class=example>
<p>The <a href="http://www.w3.org/TR/CSS2/sample.html">default style sheet for HTML&nbsp;4.0</a>
in the appendix illustrates the use of these values for HTML&nbsp;4.0:

<pre>
table    { display: table }
tr       { display: table-row }
thead    { display: table-header-group }
tbody    { display: table-row-group }
tfoot    { display: table-footer-group }
col      { display: table-column }
colgroup { display: table-column-group }
td, th   { display: table-cell }
caption  { display: table-caption }
</pre>
</div>

<p>User agents may ignore these
'display' property values for
HTML table elements, since HTML tables may be rendered using other
algorithms intended for backwards compatible rendering. However, this
is not meant to discourage the use of 'display: table' on other,
non-table elements in HTML.

<p class=issue>Remove the above paragraph?

<h3 id="anonymous-boxes">Anonymous table objects</h3>

<p>Document languages other than HTML may not contain all the elements
in the CSS&nbsp;2.1 table model. In these cases, the “missing”
elements must be assumed in order for the table model to work. Any
table element will automatically generate necessary anonymous table
objects around itself, 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 generate
<em>anonymous</em> objects (e.g., anonymous
boxes in visual table layout) according to the followin
8096
g rules:

<ol>
  <li>If the parent P of a ''table-cell'' box T is not a
  ''table-row'', a box corresponding to a ''table-row'' will be
  generated between P and T. This box will span all consecutive
  'table-cell' sibling boxes of T.

  <li>If the parent P of a ''table-row'' box T is not a ''table'',
  ''inline-table'', ''table-header-group'', ''table-footer-group'' or
  ''table-row-group'' box, a box corresponding to a ''table''
  element will be generated between P and T.
  If P is an ''inline'' box, then the generated box must be an
  ''inline-table'' box instead of a ''table'' box.
  This box will span all
  consecutive sibling boxes of T that require a
  ''table'' parent: ''table-row'', ''table-row-group'',
  ''table-header-group'', ''table-footer-group'', ''table-column'',
  ''table-column-group'', and ''table-caption''. T and T's siblings may
  also be anonymous ''table-row'' boxes generated by rule&nbsp;1.

  <li>If the parent P of a ''table-column'' box T is not a ''table'',
  ''inline-table'', or ''table-column-group'' box, a box
  corresponding to a ''table'' element will be generated between P and
  T.
  If P is an ''inline'' box, then the generated box must be an
  ''inline-table'' box instead of a ''table'' box.
  This box will span all consecutive sibling boxes
  of T that require a ''table'' parent: ''table-row'',
  ''table-row-group'', ''table-header-group'', ''table-footer-group'',
  ''table-column'', ''table-column-group'', and ''table-caption'', including
  any anonymous ''table-row'' boxes generated by rule&nbsp;1.

  <li>If the parent P of a ''table-row-group'' (or ''table-header-group'',
  ''table-footer-group'', or ''table-column-group'' or ''table-caption'')
  box T is not a ''table'' or ''inline-table'', a box
  corresponding to a ''table'' element will be generated between P and
  T.
  If P is an ''inline'' box, then the generated box must be an
  ''inline-table'' box instead of a ''table'' box.
  This box will span all consecutive sibling boxess
  of T that require a ''table'' parent: ''table-row'',
  ''table-row-group'', ''table-header-group'', ''table-footer-group'',
  ''table-column'', ''table-column-group'', and ''table-caption'', including
  any anonymous ''table-row'' boxes generated by rule&nbsp;1.

  <li>If a child T of a ''table'' box (or ''inline-table'') P is not a
  ''table-row-group'', ''table-header-group'', ''table-footer-group'',
  ''table-caption'', ''table-column'', ''table-column-group'' or ''table-row''
  box, a box corresponding to a ''table-row'' element will be
  generated between P and T. This box spans all consecutive
  siblings of T that are not ''table-row-group'', ''table-header-group'',
  ''table-footer-group'', ''table-caption'', ''table-column'',
  ''table-column-group'' or ''table-row'' boxes.

  <li>If a child T of a ''table-row-group'' box (or
  ''table-header-group'' or ''table-footer-group'') P is not a ''table-row''
  box, a box corresponding to a ''table-row'' element will be
  generated between P and T. This box spans all consecutive
  siblings of T that are not ''table-row'' boxes.

  <li>If a child T of a ''table-row'' box P is not a ''table-cell''
  box, a box corresponding to a ''table-cell'' element will be
  generated between P and T. This box spans all consecutive
  siblings of T that are not ''table-cell'' boxes.
</ol>

<div class="example">
<p>In this XML example, a ''table'' element is assumed to contain the
HBOX element:

<pre>
&lt;HBOX&gt;
  &lt;VBOX&gt;George&lt;/VBOX&gt;
  &lt;VBOX&gt;4287&lt;/VBOX&gt;
  &lt;VBOX&gt;1998&lt;/VBOX&gt;
&lt;/HBOX&gt;
</pre>

<p>because the associated style sheet is:

<pre>
HBOX { display: table-row }
VBOX { display: table-cell }
</pre>
</div>

<div class="example">
<p>In this example, three ''table-cell'' elements are assumed to contain
the text in the ROWs. Note that the text is further encapsulated in
anonymous inline boxes, as explained in <span
class="issue">[where?]</span>:

<pre class="xml-example">
&lt;STACK&gt;
  &lt;ROW&gt;This is the &lt;D&gt;top&lt;/D&gt; row.&lt;/ROW&gt;
  &lt;ROW&gt;This is the &lt;D&gt;middle&lt;/D&gt; row.&lt;/ROW&gt;
  &lt;ROW&gt;This is the &lt;D&gt;bottom&lt;/D&gt; row.&lt;/ROW&gt;
&lt;/STACK&gt;
</pre>

<p>The style sheet is:

<pre>
STACK { display: inline-table }
ROW   { display: table-row }
D     { display: inline; font-weight: bolder }
</pre>
</div>

<h2 id=columns>Columns</h2>

<p>Table cells may belong to two contexts: rows and columns. However,
in the source document cells are descendants of rows, never of
columns. Nevertheless, some aspects of cells can be influenced by
setting properties on columns.

<p>The following properties apply to column and column-group elements:
<dl>
  <dt>'border'