In this order: optionally a caption element, followed by zero or more
colgroup elements, followed optionally by a thead element, followed by
either zero or more tbody elements or one or more tr elements, followed
optionally by a tfoot element, optionally intermixed with one or more
script-supporting elements.
The table element represents data with more than one dimension, in
the form of a table.
The table element takes part in the table
model. Tables have rows, columns, and cells given by their descendants. The rows and
columns form a grid; a table's cells must completely cover that grid without overlap.
Precise rules for determining whether this conformance requirement is met are
described in the description of the table model.
Authors are encouraged to provide information describing how to interpret complex tables.
Guidance on how to provide such information is given
below.
Tables must not be used as layout aids. Historically, some web authors have misused tables in
HTML as a way to control their page layout. This usage is non-conforming, because tools attempting
to extract tabular data from such documents would obtain very confusing results. In particular,
users of accessibility tools like screen readers are likely to find it very difficult to navigate
pages with tables used for layout.
There are a variety of alternatives to using HTML tables for layout, such as CSS
grid layout, CSS flexible box layout ("flexbox"), CSS multi-column layout, CSS positioning, and
the CSS table model. [CSS]
Tables can be complicated to understand and navigate. To help users with this, user agents
should clearly delineate cells in a table from each other, unless the user agent has classified
the table as a (non-conforming) layout table.
Authors and implementers are encouraged to consider
using some of the table design techniques described below
to make tables easier to navigate for users.
User agents, especially those that do table analysis on arbitrary content, are encouraged to
find heuristics to determine which tables actually contain data and which are merely being used
for layout. This specification does not define a precise heuristic, but the following are
suggested as possible indicators:
Not a good indicator (both layout and non-layout tables have historically been given this attribute)
It is quite possible that the above suggestions are wrong. Implementers are urged
to provide feedback elaborating on their experiences with trying to create a layout table
detection heuristic.
If a table element has a (non-conforming) summary attribute, and the user agent has not classified the
table as a layout table, the user agent may report the contents of that attribute to the user.
Creates a tr element, along with a tbody if required, inserts them
into the table at the position given by the argument, and returns the tr.
The position is relative to the rows in the table. The index −1, which is the default
if the argument is omitted, is equivalent to inserting at the end of the table.
If the given position is less than −1 or greater than the number of rows, throws an
"IndexSizeError"DOMException.
Removes the tr element with the given position in the table.
The position is relative to the rows in the table. The index −1 is equivalent to
deleting the last row of the table.
If the given position is less than −1 or greater than the index of the last row, or if
there are no rows, throws an "IndexSizeError"DOMException.
In all of the following attribute and method definitions, when an element is to be
table-created, that means to create an element given the
table element's node document, the given local name, and the HTML
namespace.
The caption
IDL attribute must return, on getting, the first caption element child of the
table element, if any, or null otherwise. On setting, the first caption
element child of the table element, if any, must be removed, and the new value, if
not null, must be inserted as the first node of the table element.
The createCaption() method must return the first
caption element child of the table element, if any; otherwise a new
caption element must be table-created, inserted as the first node of the
table element, and then returned.
The deleteCaption() method must remove the first
caption element child of the table element, if any.
The tHead IDL
attribute must return, on getting, the first thead element child of the
table element, if any, or null otherwise. On setting, if the new value is null or a
thead element, the first thead element child of the table
element, if any, must be removed, and the new value, if not null, must be inserted immediately
before the first element in the table element that is neither a caption
element nor a colgroup element, if any, or at the end of the table if there are no
such elements. If the new value is neither null nor a thead element, then a
"HierarchyRequestError"DOMException must be thrown
instead.
The createTHead() method must return the first
thead element child of the table element, if any; otherwise a new
thead element must be table-created and inserted immediately before the
first element in the table element that is neither a caption element nor
a colgroup element, if any, or at the end of the table if there are no such elements,
and then that new element must be returned.
The deleteTHead() method must remove the first
thead element child of the table element, if any.
The tFoot IDL
attribute must return, on getting, the first tfoot element child of the
table element, if any, or null otherwise. On setting, if the new value is null or a
tfoot element, the first tfoot element child of the table
element, if any, must be removed, and the new value, if not null, must be inserted at the end of
the table. If the new value is neither null nor a tfoot element, then a
"HierarchyRequestError"DOMException must be thrown
instead.
The createTFoot() method must return the first
tfoot element child of the table element, if any; otherwise a new
tfoot element must be table-created and inserted at the end of the
table, and then that new element must be returned.
The deleteTFoot() method must remove the first
tfoot element child of the table element, if any.
The tBodies
attribute must return an HTMLCollection rooted at the table node, whose
filter matches only tbody elements that are children of the table
element.
The createTBody() method must table-create a new tbody element, insert it immediately
after the last tbody element child in the table element, if any, or at
the end of the table element if the table element has no
tbody element children, and then must return the new tbody element.
The rows
attribute must return an HTMLCollection rooted at the table node, whose
filter matches only tr elements that are either children of the table
element, or children of thead, tbody, or tfoot elements
that are themselves children of the table element. The elements in the collection
must be ordered such that those elements whose parent is a thead are included first,
in tree order, followed by those elements whose parent is either a table
or tbody element, again in tree order, followed finally by those
elements whose parent is a tfoot element, still in tree order.
The behavior of the insertRow(index) method depends on the state
of the table. When it is called, the method must act as required by the first item in the
following list of conditions that describes the state of the table and the index
argument:
If index is less than −1 or greater than the number of elements
in rows collection:
If the rows collection has zero elements in it, and the
table has no tbody elements in it:
The method must table-create a tbody
element, then table-create a tr element, then
append the tr element to the tbody element, then append the
tbody element to the table element, and finally return the
tr element.
The method must table-create a tr element,
append it to the last tbody element in the table, and return the tr
element.
If index is −1 or equal to the number of items in rows collection:
The method must table-create a tr element,
and append it to the parent of the last tr element in the rows collection. Then, the newly created tr element
must be returned.
Otherwise:
The method must table-create a tr element,
insert it immediately before the indexth tr element in the rows collection, in the same parent, and finally must return the
newly created tr element.
When the deleteRow(index) method is called, the user
agent must run the following steps:
If index is less than −1 or greater than or equal to the number of
elements in the rows collection, then throw an
"IndexSizeError"DOMException.
If index is −1, then remove
the last element in the rows collection from its parent, or
do nothing if the rows collection is empty.
Otherwise, remove the indexth element
in the rows collection from its parent.
Here is an example of a table being used to mark up a Sudoku puzzle. Observe the lack of
headers, which are not necessary in such a table.
For tables that consist of more than just a grid of cells with headers
in the first row and headers in the first column, and for any table in general where the reader
might have difficulty understanding the content, authors should include explanatory information
introducing the table. This information is useful for all users, but is especially useful for
users who cannot see the table, e.g. users of screen readers.
Such explanatory information should introduce the purpose of the table, outline its basic cell
structure, highlight any trends or patterns, and generally teach the user how to use the
table.
For instance, the following table:
Characteristics with positive and negative sides
Negative
Characteristic
Positive
Sad
Mood
Happy
Failing
Grade
Passing
...might benefit from a description explaining the way the table is laid out, something like
"Characteristics are given in the second column, with the negative side in the left column and the
positive side in the right column".
There are a variety of ways to include this information, such as:
In prose, surrounding the table
<p>In the following table, characteristics are given in the second
column, with the negative side in the left column and the positive
side in the right column.</p><table><caption>Characteristics with positive and negative sides</caption><thead><tr><thid="n"> Negative
<th> Characteristic
<th> Positive
<tbody><tr><tdheaders="n r1"> Sad
<thid="r1"> Mood
<td> Happy
<tr><tdheaders="n r2"> Failing
<thid="r2"> Grade
<td> Passing
</table>
<table><caption><strong>Characteristics with positive and negative sides.</strong><p>Characteristics are given in the second column, with the
negative side in the left column and the positive side in the right
column.</p></caption><thead><tr><thid="n"> Negative
<th> Characteristic
<th> Positive
<tbody><tr><tdheaders="n r1"> Sad
<thid="r1"> Mood
<td> Happy
<tr><tdheaders="n r2"> Failing
<thid="r2"> Grade
<td> Passing
</table>
<table><caption><strong>Characteristics with positive and negative sides.</strong><details><summary>Help</summary><p>Characteristics are given in the second column, with the
negative side in the left column and the positive side in the right
column.</p></details></caption><thead><tr><thid="n"> Negative
<th> Characteristic
<th> Positive
<tbody><tr><tdheaders="n r1"> Sad
<thid="r1"> Mood
<td> Happy
<tr><tdheaders="n r2"> Failing
<thid="r2"> Grade
<td> Passing
</table>
<figure><figcaption>Characteristics with positive and negative sides</figcaption><p>Characteristics are given in the second column, with the
negative side in the left column and the positive side in the right
column.</p><table><thead><tr><thid="n"> Negative
<th> Characteristic
<th> Positive
<tbody><tr><tdheaders="n r1"> Sad
<thid="r1"> Mood
<td> Happy
<tr><tdheaders="n r2"> Failing
<thid="r2"> Grade
<td> Passing
</table></figure>
<figure><figcaption><strong>Characteristics with positive and negative sides</strong><p>Characteristics are given in the second column, with the
negative side in the left column and the positive side in the right
column.</p></figcaption><table><thead><tr><thid="n"> Negative
<th> Characteristic
<th> Positive
<tbody><tr><tdheaders="n r1"> Sad
<thid="r1"> Mood
<td> Happy
<tr><tdheaders="n r2"> Failing
<thid="r2"> Grade
<td> Passing
</table></figure>
Authors may also use other techniques, or combinations of the above techniques, as
appropriate.
The best option, of course, rather than writing a description explaining the way the table is
laid out, is to adjust the table such that no explanation is needed.
In the case of the table used in the examples above, a simple rearrangement of the table so
that the headers are on the top and left sides removes the need for an explanation as well as
removing the need for the use of headers attributes:
<table><caption>Characteristics with positive and negative sides</caption><thead><tr><th> Characteristic
<th> Negative
<th> Positive
<tbody><tr><th> Mood
<td> Sad
<td> Happy
<tr><th> Grade
<td> Failing
<td> Passing
</table>
4.9.1.2 Techniques for table design
Good table design is key to making tables more readable and usable.
In visual media, providing column and row borders and alternating row backgrounds can be very
effective to make complicated tables more readable.
For tables with large volumes of numeric content, using monospaced fonts can help users see
patterns, especially in situations where a user agent does not render the borders. (Unfortunately,
for historical reasons, not rendering borders on tables is a common default.)
In speech media, table cells can be distinguished by reporting the corresponding headers before
reading the cell's contents, and by allowing users to navigate the table in a grid fashion, rather
than serializing the entire contents of the table in source order.
Authors are encouraged to use CSS to achieve these effects.
User agents are encouraged to render tables using these techniques whenever the page does not
use CSS and the table is not classified as a layout table.
When a table element is the only content in a figure element other
than the figcaption, the caption element should be omitted in favor of
the figcaption.
A caption can introduce context for a table, making it significantly easier to understand.
Consider, for instance, the following table:
1
2
3
4
5
6
1
2
3
4
5
6
7
2
3
4
5
6
7
8
3
4
5
6
7
8
9
4
5
6
7
8
9
10
5
6
7
8
9
10
11
6
7
8
9
10
11
12
In the abstract, this table is not clear. However, with a caption giving the table's number
(for reference in the main prose) and explaining its use, it
makes more sense:
<caption><p>Table 1.
<p>This table shows the total score obtained from rolling two
six-sided dice. The first row represents the value of the first die,
the first column the value of the second die. The total is given in
the cell that corresponds to the values of the two dice.
</caption>
This provides the user with more context:
Table 1.
This table shows the total score obtained from rolling two
six-sided dice. The first row represents the value of the first
die, the first column the value of the second die. The total is
given in the cell that corresponds to the values of the two dice.
A colgroup element's start tag can be
omitted if the first thing inside the colgroup element is a col element,
and if the element is not immediately preceded by another colgroup element whose
end tag has been omitted. (It can't be omitted if the element
is empty.)
If the colgroup element contains no col elements, then the element
may have a span
content attribute specified, whose value must be a valid non-negative integer greater
than zero and less than or equal to 1000.
The element may have a span content attribute specified, whose value must be a
valid non-negative integer greater than zero and less than or equal to 1000.
As a child of a table element, after any
caption, colgroup, and
thead elements, but only if there are no
tr elements that are children of the
table element.
A tbody element's start tag can be omitted
if the first thing inside the tbody element is a tr element, and if the
element is not immediately preceded by a tbody, thead, or
tfoot element whose end tag has been omitted. (It
can't be omitted if the element is empty.)
A tbody element's end tag can be omitted if
the tbody element is immediately followed by a tbody or
tfoot element, or if there is no more content in the parent element.
The tbody element represents a block of rows that consist of a
body of data for the parent table element, if the tbody element has a
parent and it is a table.
Creates a tr element, inserts it into the table section at the position given by
the argument, and returns the tr.
The position is relative to the rows in the table section. The index −1, which is the
default if the argument is omitted, is equivalent to inserting at the end of the table
section.
If the given position is less than −1 or greater than the number of rows, throws an
"IndexSizeError"DOMException.
As a child of a table element, after any
caption, and colgroup
elements and before any tbody, tfoot, and
tr elements, but only if there are no other
thead elements that are children of the
table element.
The thead element represents the block of rows that consist of
the column labels (headers) and any ancillary non-header cells for the parent table
element, if the thead element has a parent and it is a table.
This example shows a thead element being used. Notice the use of both
th and td elements in the thead element: the first row is
the headers, and the second row is an explanation of how to fill in the table.
<table><caption> School auction sign-up sheet </caption><thead><tr><th><labelfor=e1>Name</label><th><labelfor=e2>Product</label><th><labelfor=e3>Picture</label><th><labelfor=e4>Price</label><tr><td>Your name here
<td>What are you selling?
<td>Link to a picture
<td>Your reserve price
<tbody><tr><td>Ms Danus
<td>Doughnuts
<td><imgsrc="https://example.com/mydoughnuts.png"title="Doughnuts from Ms Danus"><td>$45
<tr><td><inputid=e1type=textname=whorequiredform=f><td><inputid=e2type=textname=whatrequiredform=f><td><inputid=e3type=urlname=picform=f><td><inputid=e4type=numberstep=0.01min=0value=0requiredform=f></table><formid=faction="/auction.cgi"><inputtype=buttonname=addvalue="Submit"></form>
As a child of a table element, after any
caption, colgroup, thead,
tbody, and tr elements, but only if there
are no other tfoot elements that are children of the
table element.
The tfoot element represents the block of rows that consist of
the column summaries (footers) for the parent table element, if the
tfoot element has a parent and it is a table.
As a child of a table element, after any
caption, colgroup, and thead
elements, but only if there are no tbody elements that
are children of the table element.
A tr element's end tag can be omitted if the
tr element is immediately followed by another tr element, or if there is
no more content in the parent element.
Creates a td element, inserts it into the table row at the position given by the
argument, and returns the td.
The position is relative to the cells in the row. The index −1, which is the default
if the argument is omitted, is equivalent to inserting at the end of the row.
If the given position is less than −1 or greater than the number of cells, throws an
"IndexSizeError"DOMException.
Removes the td or th element with the given position in the
row.
The position is relative to the cells in the row. The index −1 is equivalent to
deleting the last cell of the row.
If the given position is less than −1 or greater than the index of the last cell, or
if there are no cells, throws an "IndexSizeError"DOMException.
The rowIndex attribute must, if this element has a parent
table element, or a parent tbody, thead, or
tfoot element and a grandparenttable element, return the index
of this tr element in that table element's rows collection. If there is no such table element,
then the attribute must return −1.
The sectionRowIndex attribute must, if this element has a
parent table, tbody, thead, or tfoot element,
return the index of the tr element in the parent element's rows collection (for tables, that's HTMLTableElement's rows collection; for table sections, that's
HTMLTableSectionElement's rows
collection). If there is no such parent element, then the attribute must return −1.
The cells
attribute must return an HTMLCollection rooted at this tr element, whose
filter matches only td and th elements that are children of the
tr element.
The insertCell(index) method must act as
follows:
If index is less than −1 or greater than the number of elements in
the cells collection, then throw an
"IndexSizeError"DOMException.
A td element's end tag can be omitted if the
td element is immediately followed by a td or th element,
or if there is no more content in the parent element.
User agents, especially in non-visual environments or where displaying the table as a 2D grid
is impractical, may give the user context for the cell when rendering the contents of a cell; for
instance, giving its position in the table model, or listing the cell's header cells
(as determined by the algorithm for assigning header cells). When a cell's header
cells are being listed, user agents may use the value of abbr
attributes on those header cells, if any, instead of the contents of the header cells
themselves.
In this example, we see a snippet of a web application consisting of a grid of editable cells
(essentially a simple spreadsheet). One of the cells has been configured to show the sum of the
cells above it. Three have been marked as headings, which use th elements instead of
td elements. A script would attach event handlers to these elements to maintain the
total.
A th element's end tag can be omitted if the
th element is immediately followed by a td or th element,
or if there is no more content in the parent element.
The header cell applies to some of the subsequent cells in the same row(s).
col
column
The header cell applies to some of the subsequent cells in the same column(s).
rowgroup
row group
The header cell applies to all the remaining cells in the row group.
colgroup
column group
The header cell applies to all the remaining cells in the column group.
The attribute's missing value default and invalid value default are both the auto state. (In this state the header cell applies to a
set of cells selected based on context.)
The th element may have an abbr content attribute specified. Its value must be an
alternative label for the header cell, to be used when referencing the cell in other contexts
(e.g. when describing the header cells that apply to a data cell). It is typically an abbreviated
form of the full header cell, but can also be an expansion, or merely a different phrasing.
The td and th elements may have a colspan content attribute specified, whose value must be a
valid non-negative integer greater than zero and less than or equal to 1000.
The td and th elements may also have a rowspan content attribute specified,
whose value must be a valid non-negative integer less than or equal to 65534. For
this attribute, the value zero means that the cell is to span all the remaining rows in the row
group.
These attributes give the number of columns and rows respectively that the cell is to span.
These attributes must not be used to overlap cells, as described in the
description of the table model.
The td and th element may have a headers content attribute specified. The headers attribute, if specified, must contain a string
consisting of an unordered set of unique space-separated tokens, none of which are
identical to another token and each of which must have the value of an ID of a th element taking part in the same table as the td or th element (as defined by the table model).
A th element with IDid is
said to be directly targeted by all td and th elements in the
same table that have headers attributes whose values include as one of their tokens
the IDid. A th element A is said to be targeted by a th or td element
B if either A is directly targeted by B or if there exists an element C that is itself
targeted by the element B and A is directly
targeted by C.
Returns the position of the cell in the row's cells list.
This does not necessarily correspond to the x-position of the cell in the table,
since earlier cells might cover multiple rows or columns.
The headers IDL attribute must reflect the content
attribute of the same name.
The cellIndex IDL attribute must, if the element has a parent
tr element, return the index of the cell's element in the parent element's cells collection. If there is no such parent element, then the
attribute must return −1.
The abbr IDL
attribute must reflect the content attribute of the same name.
4.9.12 Processing model
The various table elements and their content attributes together define the table
model.
A table consists of cells aligned on a two-dimensional grid of
slots with coordinates (x, y). The grid is finite, and is either empty or has one or more slots. If the grid
has one or more slots, then the x coordinates are always in the range 0 ≤ x < xwidth, and the y coordinates are always in the
range 0 ≤ y < yheight. If one or both of xwidth and yheight are zero, then the
table is empty (has no slots). Tables correspond to table elements.
A cell is a set of slots anchored at a slot (cellx, celly), and with
a particular width and height such that the cell covers
all the slots with coordinates (x, y) where cellx ≤ x < cellx+width and celly ≤ y < celly+height. Cells can either be data cells
or header cells. Data cells correspond to td elements, and header cells
correspond to th elements. Cells of both types can have zero or more associated
header cells.
It is possible, in certain error cases, for two cells to occupy the same slot.
A row is a complete set of slots from x=0 to x=xwidth-1, for a particular value of y. Rows usually
correspond to tr elements, though a row group
can have some implied rows at the end in some cases involving
cells spanning multiple rows.
A column is a complete set of slots from y=0 to y=yheight-1, for a particular value of x. Columns can
correspond to col elements. In the absence of col elements, columns are
implied.
A row group is a set of rows anchored at a slot (0, groupy) with a particular height such that the row group
covers all the slots with coordinates (x, y) where 0 ≤ x < xwidth and groupy ≤ y < groupy+height. Row groups correspond to
tbody, thead, and tfoot elements. Not every row is
necessarily in a row group.
A column group is a set of columns anchored at a slot (groupx, 0) with a particular width such that the column group
covers all the slots with coordinates (x, y) where groupx ≤ x < groupx+width and 0 ≤ y < yheight. Column
groups correspond to colgroup elements. Not every column is necessarily in a column
group.
A cell cannot cover slots that are from two or more row groups. It is, however, possible for a cell to be in multiple
column groups. All the slots that form part of one cell
are part of zero or one row groups and zero or more column groups.
A table model error is an error with the data represented by table
elements and their descendants. Documents must not have table model errors.
4.9.12.1 Forming a table
To determine which elements correspond to which slots in a table associated with a table element, to determine the
dimensions of the table (xwidth and yheight), and to determine if there are any table model errors, user agents must use the following algorithm:
Let xwidth be zero.
Let yheight be zero.
Let pending tfoot elements be a list of tfoot
elements, initially empty.
Let the table be the table represented
by the table element. The xwidth and yheight variables give the table's
dimensions. The table is initially empty.
If the table element has no children elements, then return the
table (which will be empty).
Associate the first caption element child of the table element with
the table. If there are no such children, then it has no associated
caption element.
Let the current element be the first element child of the
table element.
If a step in this algorithm ever requires the current element to be advanced to the next child of the table when
there is no such next child, then the user agent must jump to the step labeled end, near
the end of this algorithm.
While the current element is not one of the following elements, advance the current element to the next
child of the table:
If the result of parsing the value is not an error or zero, then let span be that value.
Otherwise, if the col element has no span attribute, or if trying to parse the attribute's value
resulted in an error or zero, then let span be 1.
If span is greater than 1000, let it be 1000 instead.
Increase xwidth by span.
Let the last spancolumns in
the table correspond to the current columncol element.
If current column is not the last col element child of
the colgroup element, then let the current column be the
next col element child of the colgroup element, and return to
the step labeled columns.
Let all the last columns in the
table from x=xstart to
x=xwidth-1 form a new column group, anchored at the slot (xstart, 0), with width xwidth-xstart, corresponding to the colgroup element.
If the current element has no col element children
If the result of parsing the value is not an error or zero, then let span be that value.
Otherwise, if the colgroup element has no span attribute, or if trying to parse the attribute's
value resulted in an error or zero, then let span be 1.
If span is greater than 1000, let it be 1000 instead.
Increase xwidth by span.
Let the last spancolumns in
the table form a new column
group, anchored at the slot (xwidth-span, 0), with width span, corresponding to the colgroup element.
Advance the current element
to the next child of the table.
While the current element is not one of the following elements, advance the current element to the
next child of the table:
If the current element is a tr, then run the algorithm
for processing rows, advance the current element to the next child of the table, and return to the
step labeled rows.
If the current element is a tfoot, then add that element to
the list of pending tfoot elements, advance the current element to the next
child of the table, and return to the step labeled rows.
If yheight > ystart, then let all the last rows in the table from y=ystart to y=yheight-1 form a new row
group, anchored at the slot with coordinate (0, ystart), with height yheight-ystart, corresponding
to the element being processed.
If the tr element being processed has no td or th
element children, then increase ycurrent by 1, abort
this set of steps, and return to the algorithm above.
Let current cell be the first td or th element child
in the tr element being processed.
Cells: While xcurrent is less than xwidth and the slot with coordinate (xcurrent, ycurrent) already has a
cell assigned to it, increase xcurrent by 1.
If xcurrent is equal to xwidth, increase xwidth by 1. (xcurrent is never greater than xwidth.)
If parsing that value failed or if the attribute is absent, then let rowspan be 1, instead.
If rowspan is greater than 65534, let it be 65534 instead.
If rowspan is zero and the table element's
node document is not set to quirks mode, then let cell grows
downward be true, and set rowspan to 1. Otherwise, let cell grows downward be false.
If xwidth < xcurrent+colspan, then let xwidth be xcurrent+colspan.
If yheight < ycurrent+rowspan, then let yheight be ycurrent+rowspan.
Let the slots with coordinates (x, y) such that xcurrent ≤ x < xcurrent+colspan and ycurrent ≤ y < ycurrent+rowspan be covered by a
new cellc, anchored at (xcurrent, ycurrent),
which has width colspan and height rowspan,
corresponding to the current cell element.
If the current cell element is a th element, let this new
cell c be a header cell; otherwise, let it be a data cell.
If any of the slots involved already had a cell covering
them, then this is a table model error. Those slots now have two cells
overlapping.
If cell grows downward is true, then add the tuple {c, xcurrent, colspan}
to the list of downward-growing cells.
Increase xcurrent by colspan.
If current cell is the last td or th element child in
the tr element being processed, then increase ycurrent by 1, abort this set of steps, and return to the algorithm
above.
Let current cell be the next td or th element child
in the tr element being processed.
Return to the step labeled cells.
When the algorithms above require the user agent to run the algorithm for growing
downward-growing cells, the user agent must, for each {cell, cellx, width} tuple in the list of downward-growing cells, if any, extend the cellcell so that it also covers the slots with
coordinates (x, ycurrent), where cellx ≤ x < cellx+width.
4.9.12.2 Forming relationships between data cells and header cells
Each cell can be assigned zero or more header cells. The algorithm for assigning header
cells to a cell principal cell is as follows.
Let header list be an empty list of cells.
Let (principalx, principaly) be the coordinate of the slot to which the principal
cell is anchored.
If the principal cell has a headers attribute specified
For each token in the id list, if the
first element in the Document with an ID equal to
the token is a cell in the same table, and that cell is not the
principal cell, then add that cell to header list.
If principal cell does not have a headers attribute specified
Let principalwidth be the width of the principal cell.
Let principalheight be the height of the principal cell.
For each value of y from principaly to principaly+principalheight-1, run
the internal algorithm for scanning and assigning header cells, with the principal cell, the header list, the initial coordinate
(principalx, y), and the
increments Δx=−1 and Δy=0.
For each value of x from principalx to principalx+principalwidth-1, run
the internal algorithm for scanning and assigning header cells, with the principal cell, the header list, the initial coordinate
(x, principaly), and the
increments Δx=0 and Δy=−1.
If the principal cell is anchored in a row group, then add all header cells that are row group headers and are anchored in the same row group
with an x-coordinate less than or equal to principalx+principalwidth-1 and a y-coordinate less than or
equal to principaly+principalheight-1 to header
list.
If the principal cell is anchored in a column group, then add all header cells that are column group headers and are anchored in the same column
group with an x-coordinate less than or equal to principalx+principalwidth-1 and a y-coordinate less than or
equal to principaly+principalheight-1 to header
list.
Remove principal cell from the header list if it is
there.
Assign the headers in the header list to the principal
cell.
The internal algorithm for scanning and assigning header cells, given a principal cell, a header list, an initial coordinate (initialx, initialy),
and Δx and Δy increments, is as follows:
Let x equal initialx.
Let y equal initialy.
Let opaque headers be an empty list of cells.
If principal cell is a header cell
Let in header block be true, and let headers from
current header block be a list of cells containing just the principal
cell.
Otherwise
Let in header block be false and let headers from
current header block be an empty list of cells.
Loop: Increment x by Δx; increment y by Δy.
For each invocation of this algorithm, one of Δx and
Δy will be −1, and the other will be 0.
If either x or y are less than 0, then abort this
internal algorithm.
If there is no cell covering slot (x, y), or if there
is more than one cell covering slot (x, y), return to
the substep labeled loop.
Let current cell be the cell covering slot (x, y).
If current cell is a header cell
Set in header block to true.
Add current cell to headers from current header
block.
Let blocked be false.
If Δx is 0
If there are any cells in the opaque headers list anchored with the
same x-coordinate as the current cell, and with
the same width as current cell, then let blocked
be true.
If the current cell is not a column header, then let
blocked be true.
If Δy is 0
If there are any cells in the opaque headers list anchored with the
same y-coordinate as the current cell, and with
the same height as current cell, then let blocked
be true.
If the current cell is not a row header, then let blocked be true.
If blocked is false, then add the current cell
to the header list.
If current cell is a data cell and in header block is true
Set in header block to false. Add all the cells in headers from current header block to the opaque headers
list, and empty the headers from current header block list.
Return to the step labeled loop.
A header cell anchored at the slot with coordinate (x, y) with width
width and height height is said to be a column header if any of
the following are true:
the cell's scope attribute is in the column state; or
the cell's scope attribute is in the auto state, and there are no data cells in any of the
cells covering slots with y-coordinates y .. y+height-1.
A header cell anchored at the slot with coordinate (x, y) with width
width and height height is said to be a row header if any of the
following are true:
the cell's scope attribute is in the row state; or
the cell's scope attribute is in the auto state, the cell is not a column
header, and there are no data cells in any of the cells covering slots with
x-coordinates x .. x+width-1.
A header cell is said to be a column group header if its scope attribute is in the column group state.
A header cell is said to be a row group header if its scope attribute is in the row group state.