Contents
This section is normative.
The Tables Module provides elements for marking up tabular information in a document.
The module supports the following elements, attributes, and content model:
Elements | Attributes | Minimal Content Model |
---|---|---|
table | Common, summary (Text) | caption?, ( col* | colgroup* ), (( thead?, tfoot?, tbody+ ) | ( tr+ )) |
caption | Common | (PCDATA | Inline)* |
col | Common, span (Number) | EMPTY |
colgroup | Common, span (Number) | col* |
thead | Common | tr+ |
tfoot | Common | tr+ |
tbody | Common | tr+ |
tr | Common | ( td | th)+ |
td | Common, abbr (Text), axis (CDATA), colspan (Number), headers (IDREFS), rowspan (Number), scope ("row", "col", "rowgroup", "colgroup") | (PCDATA | Flow)* |
th | Common, abbr (Text), axis (CDATA), colspan (Number), headers (IDREFS), rowspan (Number), scope ("row", "col", "rowgroup", "colgroup") | (PCDATA | Flow)* |
When this module is used, it adds the table element to the Block content set of the Text Module.
Implementation: DTD
Attributes
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. The example below illustrates the use of the summary attribute.
User agents must provide access to the content of the summary attribute. As an example, access could be provided through a menu option, a mouse-over function, or through a dialog.
The following example demonstrates the difference between a table caption and a table summary.
<table summary="The table defines the class roster. The columns contain the following data: students name, permanent address, permanent phone, local address, local phone, declared major, assigned academic advisor, student standing"> <caption>Student Class Roster</caption> ...the rest of the table... </table>
Visual user agents must 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.
Attributes
Values mean the following:
User agents must ignore this attribute if the colgroup element contains one or more col elements.
The colgroup element allows authors to create structural divisions within a table. Authors may highlight this structure through style sheets. For example, the author may wish to divide the columns into logical groups such as the student's permanent address, phone number and emergency contact information. And group the student's local address, phone and email address into another logical group.
A table may either contain a single implicit column group (no colgroup element delimits the columns) or any number of explicit column groups (each delimited by an instance of the colgroup element).
The col element allows authors to share attributes among several columns without implying any structural grouping. The "span" of the col element is the number of columns that will share the element's attributes. For example, the author may wish to apply a specific style to the student's permanent data and apply a different style to the student's local data.
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 colgroup element is that authors may logically group multiple columns. By grouping columns, the author can apply rules across the entire group. The author can also apply column width balancing across the group of columns. For example, if the author has a table with five columns and the author divides the table into two column groups, one with three columns and the other with two columns. The author could define the first column group to consume 300 pixels and the second column group to consume 100 pixels. Each column within the first column group would be 100 pixels wide and the remaining two columns would be 50 pixels wide. If the author added embedded col elements, she could force one or more columns to be a specific width and the remaining columns within the group would be evenly divided within the remaining allotted width.
For example, the following table defines a column group and embedded columns with differing widths.
<style type="text/css"> #colgrp1 {width: 300} #col1 {width: 100} #col2 {width: 50} </style> ... <table> <colgroup id="colgrp1"> <col id="col1" span="3"> <col id="col2" span="2"> </colgroup> ...the rest of the table... </table>
In this example, the defined width for the colgroup constrains all of the columns to fit within that value regardless of the of the defined values within the col eleemnts. In this example, the width of the columns within the column group must be constrained to fit the defined width of the column group.
When it is necessary to single out a column (e.g., for style information, to specify width information, etc.) within a group, authors must identify that column with a col element.
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).
There are two ways to determine the number of columns in a table (in order of precedence):
It is an error if a table contains colgroup or col elements and the two calculations do not result in the same number of columns.
Once the user agent has calculated the number of columns in the table, it may group them into a colgroup.
Attributes
The table element contains all other elements that specify the caption, column groups, columns, rows, and content for a table.
The following informative list describes what operations visual user agents may carry out when rendering a table:
The XHTML 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, 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 row zero is at the top.
When a user agent allots extra cells to a row, 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.
This section provides more detailed discussion on cell header data and how non-visual agents may utilize that information.
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 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> <tbody> <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> <tr> <td headers="t1">T. Sexton</td> <td headers="t2">10</td> <td headers="t3">Espresso</td> <td headers="t4">No</td> </tr> <tr> <td headers="t1">J. Dinnen</td> <td headers="t2">5</td> <td headers="t3">Decaf</td> <td headers="t4">Yes</td> </tr> </tbody> </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 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> <tbody> <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> <tr> <td>T. Sexton</td> <td>10</td> <td>Espresso</td> <td>No</td> </tr> <tr> <td>J. Dinnen</td> <td>5</td> <td>Decaf</td> <td>Yes</td> </tbody> </table>
Here's a somewhat more complex example illustrating other values for the scope attribute:
<table summary="History courses offered in the community of Bath arranged by course name, tutor, summary, code, and fee"> <tbody> <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> </tbody> </table>
A graphical user agent might render this as:
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 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 summary="This table summarizes travel expenses incurred during August trips to San Jose and Seattle"> <caption>Travel Expense Report</caption> <tbody> <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> </tbody> </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. A user agent speaking this information might read it:
Location: San Jose. Date: 25-Aug-1997. Expenses, Meals: 37.74 Location: San Jose. Date: 26-Aug-1997. Expenses, Meals: 27.28
or, more compactly:
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 authors 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.
<table summary="Calendar for 2002."> <caption><b>Calendar for 2002</b></caption> <colgroup span="7"> <colgroup span="7"> <colgroup span="7"> <thead> <tr> <th colspan="7">January</th> <th colspan="7">February</th> <th colspan="7">March</th> </tr> </thead> <tbody> <tr> <td>S</td><td>M</td><td>T</td><td>W</td><td>T</td><td>F</td><td>S</td> <td>S</td><td>M</td><td>T</td><td>W</td><td>T</td><td>F</td><td>S</td> <td>S</td><td>M</td><td>T</td><td>W</td><td>T</td><td>F</td><td>S</td> </tr> </tbody> <tbody> <tr> <td></td><td></td><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td> <td></td><td></td><td></td><td></td><td></td><td>1</td><td>2</td> <td></td><td></td><td></td><td></td><td></td><td>1</td><td>2</td> </tr> <tr> <td>6</td><td>7</td><td>8</td><td>9</td><td>10</td><td>11</td><td>12</td> <td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td> <td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td> </tr> <tr> <td>13</td><td>14</td><td>15</td><td>16</td><td>17</td><td>18</td><td>19</td> <td>10</td><td>11</td><td>12</td><td>13</td><td>14</td><td>15</td><td>16</td> <td>10</td><td>11</td><td>12</td><td>13</td><td>14</td><td>15</td><td>16</td> </tr> <tr> <td>20</td><td>21</td><td>22</td><td>23</td><td>24</td><td>25</td><td>26</td> <td>17</td><td>18</td><td>19</td><td>20</td><td>21</td><td>22</td><td>23</td> <td>17</td><td>18</td><td>19</td><td>20</td><td>21</td><td>22</td><td>23</td> </tr> <tr> <td>27</td><td>28</td><td>29</td><td>30</td><td>31</td><td></td><td></td> <td>24</td><td>25</td><td>26</td><td>27</td><td>28</td><td></td><td></td> <td>24</td><td>25</td><td>26</td><td>27</td><td>28</td><td>29</td><td>30</td> </tr> <tr> <td></td><td></td><td></td><td></td><td></td><td></td><td></td> <td></td><td></td><td></td><td></td><td></td><td></td><td></td> <td>31</td><td></td><td></td><td></td><td></td><td></td><td></td> </tr> </tbody> </table>
would be rendered something like this:
Calendar for 2002 =================================================================== January | February | March S M T W T F S | S M T W T F S | S M T W T F S ------------------------------------------------------------------- 1 2 3 4 5 | 1 2 | 1 2 6 7 8 9 10 11 12 | 3 4 5 6 7 8 9 | 3 4 5 6 7 8 9 13 14 15 16 17 18 19 | 10 11 12 13 14 15 16| 10 11 12 13 14 15 16 20 21 22 23 24 25 26 | 17 18 19 20 21 22 23| 17 18 19 20 21 22 23 27 28 29 30 31 | 24 25 26 27 28 | 24 25 26 27 28 29 30 | | 31 ===================================================================
A graphical user agent might render this as:
This example illustrates how colgroup can be used to group columns and set the default column alignment. Similarly, tbody is used to group rows.
Attributes
The tbody element contains rows of table data. In tables that also contain thead or tfoot elements, all of these sections must contain the same number of columns.
Attributes
Table cells may contain two types of information: header information and 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> <tbody> <tr> <th>Name</th> <th>Cups</th> <th>Type of Coffee</th> <th>Sugar?</th> </tr> <tr> <td>T. Sexton</td> <td>10</td> <td>Espresso</td> <td>No</td> </tr> <tr> <td>J. Dinnen</td> <td>5</td> <td>Decaf</td> <td>Yes</td> </tbody> </table>
A user agent rendering to a tty device might display this 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 column.
<table> <caption>Cups of coffee consumed by each senator</caption> <tbody> <tr> <th>Name</td> <th>Cups</td> <th>Type of Coffee</td> <th>Sugar?</td> </tr> <tr> <td>T. Sexton</td> <td>10</td> <td>Espresso</td> <td>No</td> </tr> <tr> <td>J. Dinnen</td> <td>5</td> <td>Decaf</td> <td>Yes</td> </tr> <tr> <td>A. Soria</td> <td colspan="3"><em>Not available</em></td> </tr> </tbody> </table>
This table might be rendered on a tty device 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 | --------------------------------------
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> <tbody> <tr> <td>1</td> <td rowspan="2">2</td> <td>3</td> </tr> <tr> <td>4 <td>6</td> </tr> <tr> <td>7</td> <td>8</td> <td>9</td> </td></td> </tr> </tbody> </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 to a tty device as:
------------- | 1 | 2 | 3 | ----| |---- | 4 | | 6 | ----|---|---- | 7 | 8 | 9 | -------------
while a graphical user agent might render this as:
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> <tbody> <tr> <td>1</td> <td>2</td> <td>3</td> </tr> <tr> <td colspan="2">4</td> <td>6</td> </tr> <tr> <td>7</td> <td>8</td> <td>9</td> </tr> </tbody> </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 | -------------
A graphical user agent might render this as:
Defining overlapping cells is 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"> <tbody> <tr> <td>1</td> <td>2</td> <td>3</td> </tr> <tr> <td>4</td> <td rowspan="2">5</td> <td>6</td> </tr> <tr> <td colspan="2">7</td> <td>9</td> </tr> </tbody> </table>
Attributes
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.
If the thead, tfoot, and tbody elements are used, and a rowspan attriubte is used within a group, the rowspan must remain within the group boundaries of which it is defined.
This example illustrates the order and structure of the table head, foot, and bodies.
<table> <thead> <tr> ...header information...</tr> </thead> <tfoot> <tr> ...footer information...</tr> </tfoot> <tbody> <tr> ...first row of block one data...</tr> <tr> ...second row of block one data...</tr> </tbody> <tbody> <tr> ...first row of block two data...</tr> <tr> ...second row of block two data...</tr> <tr> ...third row of block two data...</tr> </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.
Attributes
The tr elements acts as a container for a row of table cells.
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> <tbody> <tr> ...A header row...</tr> <tr> ...First row of data...</tr> <tr> ...Second row of data...</tr> ...the rest of the table...</tr> </tbody> </table>