Contents
The HTML table model allows authors to arrange data -- text, preformatted text, images, links, forms, form fields, other tables, etc. -- into rows and columns of cells.
Each table may have an associated caption (see the CAPTION element) that provides a short description of the table's purpose. A longer description may also be provided (via the summary attribute) for the benefit of people using speech or Braille-based user agents.
Table rows may be grouped into a head, foot, and body sections, (via the THEAD, TFOOT and TBODY elements, respectively). Row groups convey additional structural information and may be rendered by user agents in ways that emphasize this structure. User agents may exploit the head/body/foot division to support scrolling of body sections independently of the head and foot sections. When long tables are printed, the head and foot information may be repeated on each page that contains table data.
Authors may also group columns to provide additional structural information that may be exploited by user agents. Furthermore, authors may declare column properties at the start of a table definition (via the COLGROUP and COL elements) in a way that enables user agents to render the table incrementally than having to wait for all the table data to arrive before rendering.
Table cells may either contain "header" information (see the TH element) or "data" (see the TD element). Cells may span multiple rows and columns. The HTML 4.0 table model allows authors to label each cell so that non-visual user agents may more easily communicate heading information about the cell to the user. Not only do these mechanisms greatly assist users with visual disabilities, they make it possible for multi-modal wireless browsers with limited display capabilities (e.g., Web-enabled pagers and phones) to handle tables.
Tables should not be used purely as a means to layout document content as this may present problems when rendering to non-visual media. Additionally, when used with graphics, these tables may force users to scroll horizontally to view a table designed on a system with a larger display. To minimize these problems, authors should use style sheets to control layout rather than tables.
Note: This specification includes more detailed information about tables in sections on table design rationale and implementation issues.
Here's a simple table that illustrates some of the features of the HTML table model. In "ascii art", the following table definition:
<TABLE border="border">
<CAPTION><EM>A test table with merged cells</EM></CAPTION>
<TR><TH rowspan="2"><TH colspan="2">Average
<TH rowspan="2">Red<BR>eyes
<TR><TH>height<TH>weight
<TR><TH>Males<TD>1.9<TD>0.003<TD>40%
<TR><TH rowspan="2">Females<TD>1.7<TD>0.002<TD>43%
</TABLE>
might be rendered something like this:
A test table with merged cells
/-----------------------------------------\
| | Average | Red |
| |-------------------| eyes |
| | height | weight | |
|-----------------------------------------|
| Males | 1.9 | 0.003 | |
|-----------------------------------------|
| Females | 1.7 | 0.002 | |
\-----------------------------------------/
Your user agent renders this table as follows:
| Average | Red eyes |
||
|---|---|---|---|
| height | weight | ||
| Males | 1.9 | 0.003 | 40% |
| Females | 1.7 | 0.002 | 43% |
<!ELEMENT TABLE - - (CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)> <!ATTLIST TABLE -- table element -- %attrs; -- %coreattrs, %i18n, %events -- summary %Text; #IMPLIED -- purpose/structure for speech output -- align %TAlign; #IMPLIED -- table position relative to window -- bgcolor %Color; #IMPLIED -- background color for cells -- width %Pixels; #IMPLIED -- table width relative to window -- border CDATA #IMPLIED -- controls frame width around table -- frame %TFrame; #IMPLIED -- which parts of table frame to include -- rules %TRules; #IMPLIED -- rulings between rows and cols -- cellspacing %Length; #IMPLIED -- spacing between cells -- cellpadding %Length; #IMPLIED -- spacing within cells -- >
Start tag: required, End tag: required
Attribute definitions
Attributes defined elsewhere
The TABLE element contains all other elements that specify caption, rows, content, and formatting.
The following informative list describes what operations user agents may carry out when rendering a table:
The HTML table model has been designed so that, with author assistance, user agents may render tables incrementally (i.e., as table rows arrive) rather than having to wait for all the data before beginning to render.
In order for a user agent to format a table in one pass, authors must tell the user agent:
More precisely, a user agent may render a table in a single pass when the column widths are specified using a combination of COLGROUP and COL elements. If any of the columns are specified in relative or percentage terms (see the section on calculating the width of columns), authors must also specify the width of the table itself.
The directionality of a table is either the inherited directionality (the default is left-to-right) or that specified by the dir attribute for the TABLE element.
For a left-to-right table, column zero is on the left side and row zero is at the top. For a right-to-left table, column zero is on the right side and column zero is at the top.
When a user agent allots extra cells to a row (see the section on calculating the number of columns in a table), extra row cells are added to the right of the table for left-to-right tables and to the left side for right-to-left tables.
Note that TABLE is the only element on which dir reverses the visual order of the columns; a single table row (TR) or a group of columns (COLGROUP) cannot be independently reversed.
When set for the TABLE element, the dir attribute also affects the direction of text within table cells (since the dir attribute is inherited by block-level elements).
To specify a right-to-left table, set the dir attribute as follows:
<TABLE dir="RTL"> ...the rest of the table... </TABLE>
The direction of text in individual cells can be changed by setting the dir attribute in an element that defines the cell. Please consult the section on bidirectional text for more information on text direction issues.
<!ELEMENT CAPTION - - (%inline;)* -- table caption --> <!ENTITY % CAlign "(top|bottom|left|right)"> <!ATTLIST CAPTION %attrs; -- %coreattrs, %i18n, %events -- align %CAlign; #IMPLIED -- relative to table -- >
Start tag: required, End tag: required
Attribute definitions
Attributes defined elsewhere
When present, the CAPTION element's text should describe the nature of the table. The CAPTION element is only permitted immediately after the TABLE start tag. A TABLE element may only contain one CAPTION element.
Visual user agents allow sighted people to quickly grasp the structure of the table from the headings as well as the caption. A consequence of this is that captions will often be inadequate as a summary of the purpose and structure of the table from the perspective of people relying on non-visual user agents.
Authors should therefore take care to provide additional information summarizing the purpose and structure of the table using the summary attribute of the TABLE element. This is especially important for tables without captions. Examples below illustrate the use of the summary attribute.
Visual user agents should avoid clipping any part of the table including the caption, unless a means is provided to access all parts, e.g., by horizontal or vertical scrolling. We recommend that the caption text be wrapped to the same width as the table. (See also the section on recommended layout algorithms.)
Start tag: required, End tag: optional
<!ELEMENT TBODY O O (TR)+ -- table body -->
Start tag: optional, End tag: optional
<!ATTLIST (THEAD|TBODY|TFOOT) -- table section -- %attrs; -- %coreattrs, %i18n, %events -- %cellhalign; -- horizontal alignment in cells -- %cellvalign; -- vertical alignment in cells -- >
Attributes defined elsewhere
Table rows may be grouped into a table head, table foot, and one or more table body sections, using the THEAD, TFOOT and TBODY elements, respectively. This division enables user agents to support scrolling of table bodies independently of the table head and foot. When long tables are printed, the table head and foot information may be repeated on each page that contains table data.
The table head and table foot should contain information about the table's columns. The table body should contain rows of table data.
When present, each THEAD, TFOOT, and TBODY contains a row group. Each row group must contain at least one row, defined by the TR element.
This example illustrates the order and structure of table heads, feet, and bodies.
<TABLE>
<THEAD>
<TR> ...header information...
</THEAD>
<TFOOT>
<TR> ...footer information...
</TFOOT>
<TBODY>
<TR> ...first row of block one data...
<TR> ...second row of block one data...
</TBODY>
<TBODY>
<TR> ...first row of block two data...
<TR> ...second row of block two data...
<TR> ...third row of block two data...
</TBODY>
</TABLE>
TFOOT must appear before TBODY within a TABLE definition so that user agents can render the foot before receiving all of the (potentially numerous) rows of data. The following summarizes which tags are required and which may be omitted:
Conforming user agent parsers must obey these rules for reasons of backward compatibility.
The table of the previous example could be shortened by removing certain end tags, as in:
<TABLE>
<THEAD>
<TR> ...header information...
<TFOOT>
<TR> ...footer information...
<TBODY>
<TR> ...first row of block one data...
<TR> ...second row of block one data...
<TBODY>
<TR> ...first row of block two data...
<TR> ...second row of block two data...
<TR> ...third row of block two data...
</TABLE>
The THEAD, TFOOT, and TBODY sections must contain the same number of columns.
Column groups allow authors to:
A column group may be defined explicitly (with the COLGROUP element) or implicitly (all columns not belonging to a COLGROUP). Thus, in the absence of any COLGROUP element, a table has a single implicit column group that contains all of the table's columns.
<!ELEMENT COLGROUP - O (col)* -- table column group --> <!ATTLIST COLGROUP %attrs; -- %coreattrs, %i18n, %events -- span NUMBER 1 -- default number of columns in group -- width %MultiLength; #IMPLIED -- default width for enclosed COLs -- %cellhalign; -- horizontal alignment in cells -- %cellvalign; -- vertical alignment in cells -- >
Start tag: required, End tag: optional
Attribute definitions
User agents must ignore this attribute if the current column group contains one or more COL elements.
This attribute specifies a default width for each column in the current column group. In addition to the standard pixel, percentage, and relative values, this attribute allows the special form "0*" (zero asterisk) which means that the width of the each column in the group should be the minimum width necessary to hold the column's contents. This implies that a column's entire contents must be known before its width may be correctly set. Authors should be aware that specifying "0*" will prevent visual user agents from rendering a table incrementally.
This attribute is overridden for any column in the column group whose width is specified via a COL element.
Attributes defined elsewhere
The COLGROUP element creates an explicit column group. The number of columns in the column group may be specified in two, mutually exclusive ways:
The advantage of using the span attribute is that authors may group together information about column widths. Thus, if a table contains forty columns, all of which have a width of 20 pixels, it is easier to write:
<COLGROUP span="40" width="20"> </COLGROUP>
than:
<COLGROUP>
<COL width="20">
<COL width="20">
...a total of forty COL elements...
</COLGROUP>
When it is necessary to single out a column (e.g., for style information, to specify width information) within a group, authors must identify that column by using the COL element. Thus, to apply special style information to the last column of the previous table, we single it out as follows:
<COLGROUP width="20">
<COL repeat="39">
<COL id="format-me-specially">
</COLGROUP>
The width attribute of the COLGROUP element is inherited by all 40 columns. The COL element refers to the first 39 columns (doing nothing special to them) and the second one assigns an id value to the fortieth columns so that style sheets may refer to it.
The table in the following example contains two column groups. The first column group contains 10 columns and the second contains 5 columns. The default width for each column in the first column group is 50 pixels. The width of each column in the second column group will be the minimum for the column.
<TABLE> <COLGROUP span="10" width="50"> <COLGROUP span="5" width="0*"> <THEAD> <TR><TD> ... </TABLE>
<!ELEMENT COL - O EMPTY -- table column --> <!ATTLIST COL -- column groups and properties -- %attrs; -- %coreattrs, %i18n, %events -- repeat NUMBER 1 -- repeat count for COL -- width %MultiLength; #IMPLIED -- column width specification -- %cellhalign; -- horizontal alignment in cells -- %cellvalign; -- vertical alignment in cells -- >
Start tag: required, End tag: forbidden
Attribute definitions
Attributes defined elsewhere
The COL element allows authors to group together attribute specifications for table columns. The COL does not group columns together structurally -- that is the role of the COLGROUP element. COL elements are empty and serve only as a support for attributes. They may appear inside or outside an explicit column group (i.e., COLGROUP element).
The width attribute for COL refers to the width of each column referred to by the element's repeat attribute.
There are two ways to determine the number of columns in a table (in order of precedence):
It is considered an error if these two calculations do not result in the same number of columns. Authoring tools should detect this error. If a user agent carries out the first computation, then realizes that the number of columns for a given row exceeds the number calculated for the table, it should reflow the table.
Once the user agent has calculated the number of columns in the table, it may group them into column groups.
For example, for each of the following tables, the two column calculation methods should result in three columns. The first three tables may be rendered incrementally.
<TABLE> <COLGROUP span="3"></COLGROUP> <TR><TD> ... ...rows... </TABLE> <TABLE> <COLGROUP> <COL> <COL repeat="2"> </COLGROUP> <TR><TD> ... ...rows... </TABLE> <TABLE> <COLGROUP> <COL> </COLGROUP> <COLGROUP span="2"> <TR><TD> ... ...rows... </TABLE> <TABLE> <TR> <TD><TD><TD> </TR> </TABLE>
Authors may specify column widths in three ways:
However, if the table does not have a fixed width, user agents must receive all table data before they can determine the horizontal space required by the table. Only then may this space be allotted to proportional columns.
If an author specifies no width information for a column, a user agent may not be able to incrementally format the table since it must wait for the entire column of data to arrive in order to allot an appropriate width.
If column widths prove to be too narrow for the contents of a particular table cell, user agents may choose to reflow the table.
The table in this example contains six columns. The first one does not belong to an explicit column group. The next three belong to the first explicit column group and the last two belong to the second explicit column group. This table cannot be formatted incrementally since it contains proportional column width specifications and no value for the width attribute for the TABLE element.
Once the (visual) user agent has received the table's data: the available horizontal space will be alloted by the user agent as follows: First the user agent will allot 30 pixels to columns one and two. Then, the minimal space required for the third column will be reserved. The remaining horizontal space will be divided into six equal portions (since 2* + 1* + 3* = 6 portions). Column four (2*) will receive two of these portions, column five (1*) will receive one, and column six (3*) will receive three.
<TABLE> <COLGROUP> <COL width="30"> <COLGROUP> <COL width="30"> <COL width="0*"> <COL width="2*"> <COLGROUP align="center"> <COL width="1*"> <COL width="3*" align="char" char=":"> <THEAD> <TR><TD> ... ...rows... </TABLE>
We have set the value of the align attribute in the second column group to "center". All cells in every column in this group will inherit this value, but may override it. In fact, the final COL does just that, by specifying that every cell in the column it governs will be aligned along the ":" character.
In the following table, the column width specifications allow the user agent to format the table incrementally:
<TABLE width="200"> <COLGROUP span="10" width="15"> <COLGROUP width="*"> <COL id="penultimate-row"> <COL id="last-row"> <THEAD> <TR><TD> ... ...rows... </TABLE>
The first ten columns will be 15 pixels wide each. The last two columns will each receive half of the remaining 50 pixels. Note that the COL elements appear only so that an id value may be specified for the last two columns.
<!ELEMENT TR - O (TH|TD)+ -- table row --> <!ATTLIST TR -- table row -- %attrs; -- %coreattrs, %i18n, %events -- %cellhalign; -- horizontal alignment in cells -- %cellvalign; -- vertical alignment in cells -- bgcolor %Color; #IMPLIED -- background color for row -- >
Start tag: required, End tag: optional
Attributes defined elsewhere
The TR elements acts as a container for a row of table cells. The end tag may be omitted.
This sample table contains three rows, each begun by the TR element:
<TABLE summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR> ...A header row...
<TR> ...First row of data...
<TR> ...Second row of data...
...the rest of the table...
</TABLE>
<!ELEMENT (TH|TD) - O (%flow;)* -- table header cell, table data cell --> <!-- Scope is simpler than axes attribute for common tables --> <!ENTITY % Scope "(row|col|rowgroup|colgroup)"> <!-- TH is for headers, TD for data, but for cells acting as both use TD --> <!ATTLIST (TH|TD) -- header or data cell -- %attrs; -- %coreattrs, %i18n, %events -- abbr %Text; #IMPLIED -- abbreviation for header cell -- axis CDATA #IMPLIED -- names groups of related headers-- headers IDREFS #IMPLIED -- list of id's for header cells -- scope %Scope; #IMPLIED -- scope covered by header cells -- nowrap (nowrap) #IMPLIED -- suppress word wrap -- bgcolor %Color; #IMPLIED -- cell background color -- rowspan NUMBER 1 -- number of rows spanned by cell -- colspan NUMBER 1 -- number of cols spanned by cell -- %cellhalign; -- horizontal alignment in cells -- %cellvalign; -- vertical alignment in cells -- width %Pixels; #IMPLIED -- width for cell -- height %Pixels; #IMPLIED -- height for cell -- >
Start tag: required, End tag: optional
Attribute definitions
Attributes defined elsewhere
Table cells may contain two types of information: header information and actual data. This distinction enables user agents to render header and data cells distinctly, even in the absence of style sheets. For example, visual user agents may present header cell text with a bold font. Speech synthesizers may render header information with a distinct voice inflection.
The TH element defines a cell that contains header information. User agents have two pieces of header information available: the contents of the TH element and the value of the abbr attribute. User agents must render either the contents of the cell or the value of the abbr attribute. For visual media, the latter may be appropriate when there is insufficient space to render the full contents of the cell. For non-visual media abbr may be used as an abbreviation for table headers when these are rendered along with the contents of the cells to which they apply.
The headers and scope attributes also allow authors to help non-visual user agents process header information. Please consult the section on labeling cells for non-visual user agents for information and examples.
The TD element defines a cell that contains data.
Cells may be empty (i.e., contain no data).
For example, the following table contains four columns of data, each headed by a column description.
<TABLE summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH>Name</TH>
<TH>Cups</TH>
<TH>Type of Coffee</TH>
<TH>Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
Your user agent renders the beginning of this table as follows:
| Name | Cups | Type of Coffee | Sugar? |
|---|---|---|---|
| T. Sexton | 10 | Espresso | No |
| J. Dinnen | 5 | Decaf | Yes |
Cells may span several rows or columns. The number of rows or columns spanned by a cell is set by the rowspan and colspan attributes for the TH and TD elements.
In this table definition, we specify that the cell in row four, column two should span a total of three columns, including the current row.
<TABLE border="border"> <CAPTION>Cups of coffee consumed by each senator</CAPTION> <TR><TH>Name<TH>Cups<TH>Type of Coffee<TH>Sugar? <TR><TD>T. Sexton<TD>10<TD>Espresso<TD>No <TR><TD>J. Dinnen<TD>5<TD>Decaf<TD>Yes <TR><TD>A. Soria<TD colspan="3"><em>Not available</em> </TABLE>
This table might be rendered by a visual user agent as follows:
Cups of coffee consumed by each senator -------------------------------------- | Name |Cups|Type of Coffee|Sugar?| -------------------------------------- |T. Sexton|10 |Espresso |No | -------------------------------------- |J. Dinnen|5 |Decaf |Yes | -------------------------------------- |A. Soria |Not available | --------------------------------------
In your user agent this appears as:
| Name | Cups | Type of Coffee | Sugar? |
|---|---|---|---|
| T. Sexton | 10 | Espresso | No |
| J. Dinnen | 5 | Decaf | Yes |
| A. Soria | Not available | ||
The next example illustrates (with the help of table borders) how cell definitions that span more than one row or column affect the definition of later cells. Consider the following table definition:
<TABLE border="border"> <TR><TD>1 <TD rowspan="2">2 <TD>3 <TR><TD>4 <TD>6 <TR><TD>7 <TD>8 <TD>9 </TABLE>
As cell "2" spans the first and second rows, the definition of the second row will take it into account. Thus, the second TD in row two actually defines the row's third cell. Visually, the table might be rendered something like this:
------------- | 1 | 2 | 3 | ----| |---- | 4 | | 6 | ----|---|---- | 7 | 8 | 9 | -------------
Your user agent renders this table as:
| 1 | 2 | 3 |
| 4 | 6 | |
| 7 | 8 | 9 |
Note that if the TD defining cell "6" had been omitted, an extra empty cell would have been added by the user agent to complete the row.
Similarly, in the following table definition:
<TABLE border="border"> <TR><TD>1 <TD>2 <TD>3 <TR><TD colspan="2">4 <TD>6 <TR><TD>7 <TD>8 <TD>9 </TABLE>
cell "4" spans two columns, so the second TD in the row actually defines the third cell ("6"):
------------- | 1 | 2 | 3 | --------|---- | 4 | 6 | --------|---- | 7 | 8 | 9 | -------------
Your user agent renders this table as:
| 1 | 2 | 3 |
| 4 | 6 | |
| 7 | 8 | 9 |
Defining overlapping cells is considered an error. User agents may vary in how they handle this error (e.g., rendering may vary).
The following illegal example illustrates how one might create overlapping cells. In this table, cell "5" spans two rows and cell "7" spans two columns, so there is overlap in the cell between "7" and "9":
<TABLE border="border">
<TR><TD>1 <TD>2 <TD>3
<TR><TD>4 <TD rowspan="2">5 <TD>6
<TR><TD colspan="2">7 <TD>9
</TABLE>
Note.The following sections describe the HTML table attributes that concern visual formatting. Although style sheets will offer better control of visual table formatting, at the writing of this specification, [CSS1] did not offer mechanisms to control all aspects of visual table formatting.
HTML 4.0 includes mechanisms to control:
The following attributes affect a table's external frame and internal rules.
Attribute definitions
To help distinguish the cells of a table, we can set the border attribute of the TABLE element. Consider a previous example:
<TABLE border="border"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH>Name</TH>
<TH>Cups</TH>
<TH>Type of Coffee</TH>
<TH>Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
With the addition of the border attribute, your user agent renders the beginning of this table as follows:
| Name | Cups | Type of Coffee | Sugar? |
|---|---|---|---|
| T. Sexton | 10 | Espresso | No |
| J. Dinnen | 5 | Decaf | Yes |
In the following example, the user agent should show borders five pixels thick on the left-hand and right-hand sides of the table, with rules drawn between each column.
<TABLE border="5" frame="vsides" rules="cols"> <TR> <TD>1 <TD>2 <TD>3 <TR> <TD>4 <TD>5 <TD>6 <TR> <TD>7 <TD>8 <TD>9 </TABLE>
The following settings should be observed by user agents for backwards compatibility.
For example, the following definitions are equivalent:
<TABLE border="2"> <TABLE border="2" frame="border" rules="all">
as are the following:
<TABLE border> <TABLE frame="border" rules="all">
Note. The border attribute also defines the border behavior for the OBJECT and IMG elements, but takes different values for those elements.
The following attributes may be set for different table elements (see their definitions).
<!-- horizontal alignment attributes for cell contents --> <!ENTITY % cellhalign "align (left|center|right|justify|char) #IMPLIED char %Character; #IMPLIED -- alignment char, e.g. char=':' -- charoff %Length; #IMPLIED -- offset for alignment char --" > <!-- vertical alignment attributes for cell contents --> <!ENTITY % cellvalign "valign (top|middle|bottom|baseline) #IMPLIED" >
Attribute definitions
When charoff is used to set the offset of an alignment character, the direction of offset is determined by the current text direction (set by the dir attribute). In left-to-right texts (the default), offset is from the left margin. In right-to-left texts, offset is from the right margin.
The table in this example aligns a row of currency values along a decimal point. We set the alignment character to "." explicitly.
<TABLE border="border"> <COLGROUP> <COL><COL align="char" char="."> <THEAD> <TR><TH>Vegetable <TH>Cost per kilo <TBODY> <TR><TD>Lettuce <TD>$1 <TR><TD>Silver carrots <TD>$10.50 <TR><TD>Golden turnips <TD>$100.30 </TABLE>
The formatted table should look something like this:
------------------------------ | Vegetable |Cost per kilo| |--------------|-------------| |Lettuce | $1 | |--------------|-------------| |Silver carrots| $10.50| |--------------|-------------| |Golden turnips| $100.30| ------------------------------
When the contents of a cell contain more than one instance of the alignment character specified by char and the contents wrap, user agent behavior is undefined. Authors should therefore be attentive in their use of char.
Note. Visual user agents typically render TH elements vertically and horizontally centered within the cell and with a bold font weight.
The alignment of cell contents can be specified on a cell by cell basis, or inherited from enclosing elements, such as the row, column or the table itself.
The order of precedence (from highest to lowest) for the attributes align, char, and charoff is the following:
The order of precedence (from highest to lowest) for the attribute valign (as well as the other inherited attributes lang, dir, and style) is the following:
Furthermore, when rendering cells, horizontal alignment is determined by columns in preference to rows, while for vertical alignment, rows are given preference over columns.
The default alignment for cells depends on the user agent. However, user agents should substitute the default attribute for the current directionality (i.e., not just "left" in all cases).
User agents that do not support the "justify" value of the align attribute should use the value of the inherited directionality in its place.
Attribute definitions
These two attributes control spacing between and within cells. The following illustration explains how they relate:
In the following example, the cellspacing attribute specifies that cells should be separated from each other and from the table frame by twenty pixels. The cellpadding attribute specifies that the top margin of the cell and the bottom margin of the cell will each be separated from the cell's contents by 10% of the available vertical space (the total being 20%). Similarly, the left margin of the cell and the right margin of the cell will each be separated from the cell's contents by 10% of the available horizontal space (the total being 20%).
<TABLE cellspacing="20" cellpadding="20%"> <TR> <TD>Data1 <TD>Data2 <TD>Data3 </TABLE>
If a table or given column has a fixed width, cellspacing and cellpadding may demand more space than assigned. User agents may give these attributes precedence over the width attribute when a conflict occurs, but are not required to.
Non-visual user agents such as speech synthesizers and Braille-based devices may use the following TD and TH element attributes to render table cells more intuitively:
In the following example, we assign header information to cells by setting the headers attribute. Each cell in the same column refers to the same header cell (via the id attribute).
<TABLE border="border"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH id="t1">Name</TH>
<TH id="t2">Cups</TH>
<TH id="t3" abbr="Type">Type of Coffee</TH>
<TH id="t4">Sugar?</TH>
<TR>
<TD headers="t1">T. Sexton</TD>
<TD headers="t2">10</TD>
<TD headers="t3">Espresso</TD>
<TD headers="t4">No</TD>
<TR>
<TD headers="t1">J. Dinnen</TD>
<TD headers="t2">5</TD>
<TD headers="t3">Decaf</TD>
<TD headers="t4">Yes</TD>
</TABLE>
A speech synthesizer might render this table as follows:
Caption: Cups of coffee consumed by each senator
Summary: This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.
Name: T. Sexton, Cups: 10, Type: Espresso, Sugar: No
Name: J. Dinnen, Cups: 5, Type: Decaf, Sugar: Yes
Note how the header "Type of Coffee" is abbreviated to "Type" using the abbr attribute.
Here is the same example substituting the scope attribute for the headers attribute. Note the value "col" for the scope attribute, meaning "all cells in the current column":
<TABLE border="border"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH scope="col">Name</TH>
<TH scope="col">Cups</TH>
<TH scope="col" abbr="Type">Type of Coffee</TH>
<TH scope="col">Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
Here's a somewhat more complex example illustrating other values for the scope attribute:
<TABLE border="border" cellpadding="5" cellspacing="2"
summary="History courses offered in the community of
Bath arranged by course name, tutor, summary,
code, and fee">
<TR>
<TH colspan="5" scope="colgroup">Community Courses -- Bath Autumn 1997</TH>
</TR>
<TR>
<TH scope="col" abbr="Name">Course Name</TH>
<TH scope="col" abbr="Tutor">Course Tutor</TH>
<TH scope="col">Summary</TH>
<TH scope="col">Code</TH>
<TH scope="col">Fee</TH>
</TR>
<TR>
<TD scope="row">After the Civil War</TD>
<TD>Dr. John Wroughton</TD>
<TD>
The course will examine the turbulent years in England
after 1646. <EM>6 weekly meetings starting Monday 13th
October.</EM>
</TD>
<TD>H27</TD>
<TD>£32</TD>
</TR>
<TR>
<TD scope="row">An Introduction to Anglo-Saxon England</TD>
<TD>Mark Cottle</TD>
<TD>
One day course introducing the early medieval
period reconstruction the Anglo-Saxons and
their society. <EM>Saturday 18th October.</EM>
</TD>
<TD>H28</TD>
<TD>£18</TD>
</TR>
<TR>
<TD scope="row">The Glory that was Greece</TD>
<TD>Valerie Lorenz</TD>
<TD>
Birthplace of democracy, philosophy, heartland of theater, home of
argument. The Romans may have done it but the Greeks did it
first. <EM>Saturday day school 25th October 1997</EM>
</TD>
<TD>H30</TD>
<TD>£18</TD>
</TR>
</TABLE>
Your user agent renders this table as follows:
| Community Courses -- Bath Autumn 1997 | ||||
|---|---|---|---|---|
| Course Name | Course Tutor | Summary | Code | Fee |
| After the Civil War | Dr. John Wroughton | The course will examine the turbulent years in England after 1646. 6 weekly meetings starting Monday 13th October. | H27 | £32 |
| An Introduction to Anglo-Saxon England | Mark Cottle | One day course introducing the early medieval period reconstruction the Anglo-Saxons and their society. Saturday 18th October. | H28 | £18 |
| The Glory that was Greece | Valerie Lorenz | Birthplace of democracy, philosophy, heartland of theater, home of argument. The Romans may have done it but the Greeks did it first. Saturday day school 25th October 1997 | H30 | £18 |
Note the use of the scope attribute with the "row" value. Although the first cell in each row contains data, not header information, the scope attribute makes the data cell behave like a row header cell. This allows speech synthesizers to provide the relevant course name upon request or to state it immediately before each cell's content.
Users browsing a table with a speech-based user agent may wish to hear an explanation of a cell's contents in addition to the contents themselves. One way the user might provide an explanation is by speaking associated header information before speaking the data cell's contents (see the section on associating header information with data cells).
Users may also want information about more than one cell, in which case header information provided at the cell level (by headers, scope, and abbr) may not provide adequate context. Consider the following table, which classifies expenses for meals, hotels, and transport in two locations (San Jose and Seattle) over several days:
Users might want to extract information from the table in the form of queries:
Each query involves a computation by the user agent that may involve zero or more cells. In order to determine, for example, the costs of meals on 25 August, the user agent must know which table cells refer to "Meals" (all of them) and which refer to "Dates" (specifically, 25 August), and find the intersection of the two sets.
To accommodate this type of query, the HTML 4.0 table model allows authors to place cell headers and data into categories. For example, for the travel expense table, an author could group the header cells "San Jose" and "Seattle" into the category "Location", the headers "Meals", "Hotels", and "Transport" in the category "Expenses", and the four days into the category "Date". The previous three questions would then have the following meanings:
Authors categorize a header or data cell by setting the axis attribute for the cell. For instance, in the travel expense table, the cell containing the information "San Jose" could be placed in the "Location" category as follows:
<TH id="a6" axis="location">San Jose</TH>
Any cell containing information related to "San Jose" should refer to this header cell via either the headers or the scope attribute. Thus, meal expenses for 25-Aug-1997 should be marked up to refer to id attribute (whose value here is "a6") of the "San Jose" header cell:
<TD headers="a6">37.74</TD>
Each headers attribute provides a list of id references. Authors may thus categorize a given cell in any number of ways (or, along any number of "headers", hence the name).
Below we mark up the travel expense table with category information:
<TABLE border="border"> <CAPTION> Travel Expense Report </CAPTION> <TR> <TH></TH> <TH id="a2" axis="expenses">Meals</TH> <TH id="a3" axis="expenses">Hotels</TH> <TH id="a4" axis="expenses">Transport</TH> <TD>subtotals</TD> </TR> <TR> <TH id="a6" axis="location">San Jose</TH> <TH></TH> <TH></TH> <TH></TH> <TD></TD> </TR> <TR> <TD id="a7" axis="date">25-Aug-97</TD> <TD headers="a6 a7 a2">37.74</TD> <TD headers="a6 a7 a3">112.00</TD> <TD headers="a6 a7 a4">45.00</TD> <TD></TD> </TR> <TR> <TD id="a8" axis="date">26-Aug-97</TD> <TD headers="a6 a8 a2">27.28</TD> <TD headers="a6 a8 a3">112.00</TD> <TD headers="a6 a8 a4">45.00</TD> <TD></TD> </TR> <TR> <TD>subtotals</TD> <TD>65.02</TD> <TD>224.00</TD> <TD>90.00</TD> <TD>379.02</TD> </TR> <TR> <TH id="a10" axis="location">Seattle</TH> <TH></TH> <TH></TH> <TH></TH> <TD></TD> </TR> <TR> <TD id="a11" axis="date">27-Aug-97</TD> <TD headers="a10 a11 a2">96.25</TD> <TD headers="a10 a11 a3">109.00</TD> <TD headers="a10 a11 a4">36.00</TD> <TD></TD> </TR> <TR> <TD id="a12" axis="date">28-Aug-97</TD> <TD headers="a10 a12 a2">35.00</TD> <TD headers="a10 a12 a3">109.00</TD> <TD headers="a10 a12 a4">36.00</TD> <TD></TD> </TR> <TR> <TD>subtotals</TD> <TD>131.25</TD> <TD>218.00</TD> <TD>72.00</TD> <TD>421.25</TD> </TR> <TR> <TH>Totals</TH> <TD>196.27</TD> <TD>442.00</TD> <TD>162.00</TD> <TD>800.27</TD> </TR> </TABLE>
Note that marking up the table this way also allows user agents to avoid confusing the user with unwanted information. For instance, if a speech synthesizer were to speak all of the figures in the "Meals" column of this table in response to the query "What were all my meal expenses?", a user would not be able to distinguish a day's expenses from subtotals or totals. By carefully categorizing cell data, authors allow user agents to make important semantic distinctions when rendering.
Of course, there is no limit to how authors may categorize information in a table. In the travel expense table, for example, we could add the additional categories "subtotals" and "totals".
This specification does not require user agents to handle information provided by the axis attribute, nor does it make any recommendations about how user agents may present axis information to users or how users may query the user agent about this information.
However, user agents, particularly speech synthesizers, may want to factor out information common to several cells that are the result of a query. For instance, if the user asks "What did I spend for meals in San Jose?", the user agent would first determine the cells in question (25-Aug-1997: 37.74, 26-Aug-1997:27.28), then render this information. One possible rendering of this information might be to speak:
Location: San Jose. Date: 25-Aug-1997. Expenses, Meals: 37.74 Location: San Jose. Date: 26-Aug-1997. Expenses, Meals: 27.28
Another might be less explicit:
San Jose, 25-Aug-1997, Meals: 37.74 San Jose, 26-Aug-1997, Meals: 27.28
An even more economical rendering would factor the common information and reorder it:
San Jose, Meals, 25-Aug-1997: 37.74
26-Aug-1997: 27.28
User agents that support this type of rendering should allow user agents a means to customize rendering (e.g., through style sheets).
In the absence of header information from either the scope or headers attribute, user agents may construct header information according to the following algorithm. The goal of the algorithm is to find an ordered list of headers. (In the following description of the algorithm the table directionality is assumed to be left-to-right.)
This sample illustrates grouped rows and columns. The example is adapted from "Developing International Software", by Nadine Kano.
In "ascii art", the following table:
<TABLE border="2" frame="hsides" rules="groups"> <CAPTION>CODE-PAGE SUPPORT IN MICROSOFT WINDOWS</CAPTION> <COLGROUP align="center"> <COLGROUP align="left"> <COLGROUP align="center" span="2"> <COLGROUP align="center" span="3"> <THEAD valign="top"> <TR> <TH>Code-Page<BR>ID <TH>Name <TH>ACP <TH>OEMCP <TH>Windows<BR>NT 3.1 <TH>Windows<BR>NT 3.51 <TH>Windows<BR>95 <TBODY> <TR><TD>1200<TD>Unicode (BMP of ISO/IEC-10646)<TD><TD><TD>X<TD>X<TD>* <TR><TD>1250<TD>Windows 3.1 Eastern European<TD>X<TD><TD>X<TD>X<TD>X <TR><TD>1251<TD>Windows 3.1 Cyrillic<TD>X<TD><TD>X<TD>X<TD>X <TR><TD>1252<TD>Windows 3.1 US (ANSI)<TD>X<TD><TD>X<TD>X<TD>X <TR><TD>1253<TD>Windows 3.1 Greek<TD>X<TD><TD>X<TD>X<TD>X <TR><TD>1254<TD>Windows 3.1 Turkish<TD>X<TD><TD>X<TD>X<TD>X <TR><TD>1255<TD>Hebrew<TD>X<TD><TD><TD><TD>X <TR><TD>1256<TD>Arabic<TD>X<TD><TD><TD><TD>X <TR><TD>1257<TD>Baltic<TD>X<TD><TD><TD><TD>X <TR><TD>1361<TD>Korean (Johab)<TD>X<TD><TD><TD>**<TD>X <TBODY> <TR><TD>437<TD>MS-DOS United States<TD><TD>X<TD>X<TD>X<TD>X <TR><TD>708<TD>Arabic (ASMO 708)<TD><TD>X<TD><TD><TD>X <TR><TD>709<TD>Arabic (ASMO 449+, BCON V4)<TD><TD>X<TD><TD><TD>X <TR><TD>710<TD>Arabic (Transparent Arabic)<TD><TD>X<TD><TD><TD>X <TR><TD>720<TD>Arabic (Transparent ASMO)<TD><TD>X<TD><TD><TD>X </TABLE>
would be rendered something like this:
CODE-PAGE SUPPORT IN MICROSOFT WINDOWS
===============================================================================
Code-Page | Name | ACP OEMCP | Windows Windows Windows
ID | | | NT 3.1 NT 3.51 95
-------------------------------------------------------------------------------
1200 | Unicode (BMP of ISO 10646) | | X X *
1250 | Windows 3.1 Eastern European | X | X X X
1251 | Windows 3.1 Cyrillic | X | X X X
1252 | Windows 3.1 US (ANSI) | X | X X X
1253 | Windows 3.1 Greek | X | X X X
1254 | Windows 3.1 Turkish | X | X X X
1255 | Hebrew | X | X
1256 | Arabic | X | X
1257 | Baltic | X | X
1361 | Korean (Johab) | X | ** X
-------------------------------------------------------------------------------
437 | MS-DOS United States | X | X X X
708 | Arabic (ASMO 708) | X | X
709 | Arabic (ASMO 449+, BCON V4) | X | X
710 | Arabic (Transparent Arabic) | X | X
720 | Arabic (Transparent ASMO) | X | X
===============================================================================
Your user agent renders this table as follows:
| Code-Page ID |
Name | ACP | OEMCP | Windows NT 3.1 |
Windows NT 3.51 |
Windows 95 |
|---|---|---|---|---|---|---|
| 1200 | Unicode (BMP of ISO/IEC-10646) | X | X | * | ||
| 1250 | Windows 3.1 Eastern European | X | X | X | X | |
| 1251 | Windows 3.1 Cyrillic | X | X | X | X | |
| 1252 | Windows 3.1 US (ANSI) | X | X | X | X | |
| 1253 | Windows 3.1 Greek | X | X | X | X | |
| 1254 | Windows 3.1 Turkish | X | X | X | X | |
| 1255 | Hebrew | X | X | |||
| 1256 | Arabic | X | X | |||
| 1257 | Baltic | X | X | |||
| 1361 | Korean (Johab) | X | ** | X | ||
| 437 | MS-DOS United States | X | X | X | X | |
| 708 | Arabic (ASMO 708) | X | X | |||
| 709 | Arabic (ASMO 449+, BCON V4) | X | X | |||
| 710 | Arabic (Transparent Arabic) | X | X | |||
| 720 | Arabic (Transparent ASMO) | X | X |
This example illustrates how COLGROUP can be used to group columns and set the default column alignment. Similarly, TBODY is used to group rows. The frame and rules attributes tell the user agent which borders and rules to render.