4.11. Table Cells: TH and TD

   <!ELEMENT (th|td) - O %body.content>

   <!ATTLIST (th|td)                  -- header or data cell --
           %attrs;                    -- id, lang, dir and class --
           axis    CDATA    #IMPLIED  -- defaults to cell content --
           axes    CDATA    #IMPLIED  -- list of axis names --
           nowrap (nowrap)  #IMPLIED  -- suppress word wrap --
           rowspan NUMBER   1         -- number of rows spanned by --
                                      -- cell --
           colspan NUMBER   1         -- number of cols spanned by --
                                      -- cell --
           %cell.halign;              -- horizontal alignment in --
                                      -- cells --
           %cell.valign;              -- vertical alignment in cells --
           >

TH elements are used to represent header cells, while TD elements are used to represent data cells. This allows user agents to render header and data cells distinctly, even in the absence of style sheets.

Cells can span multiple rows and columns, and may be empty. Cells spanning rows contribute to the column count on each of the spanned rows, but only appear in the markup once (in the first row spanned). The row count is determined by the number of TR elements. Any rows implied by cells spanning rows beyond this should be ignored.

If the column count for the table is greater than the number of cells for a given row (after including cells for spanned rows), the missing cells are treated as occurring on the right hand side of the table and rendered as empty cells. If the language context indicates a right to left writing order, then the missing cells should be placed on the left hand side.

It is possible to create tables with overlapping cells, for instance:

       <table border>
       <tr><td rowspan=2>1<td>2<td>3
       <tr><td rowspan=2>4
       <tr><td colspan=2>5<td>6
       </table>

which might look something like:

       /-----------\
       | 1 | 2 | 3 |
       |   |-------|
       |   | 4 |   |
       |---|...|---|
       | 5 :   | 6 |
       \-----------/

In this example, the cells labelled 4 and 5 overlap. In such cases, the rendering is implementation dependent.

The AXIS and AXES attributes for cells provide a means for defining concise labels for cells. When rendering to speech, these attributes may be used to provide abbreviated names for the headers relevant to each cell. Another application is when you want to be able to later process table contents to enter them into a database. These attributes are then used to give database field names. The table's class attribute should be used to let the software recognize which tables can be treated in this way.

ID, CLASS, LANG and DIR

See earlier description of common attributes.

AXIS

This defines an abbreviated name for a header cell, e.g. which can be used when rendering to speech. It defaults to the cell's content.

AXES

This is a comma separated list of axis names which together identify the row and column headers that pertain to this cell. It is used for example when rendering to speech to identify the cell's position in the table. If missing the user agent can try to follow up columns and left along rows (right for some languages) to find the corresponding header cells.

NOWRAP, e.g. <TD NOWRAP>

The presence of this attribute disables automatic wrapping of text lines for this cell. If used uncautiously, it may result in excessively wide cells. This attribute is defined for backwards compatibility with deployed user agents. Greater control is possible with associated style sheet languages (for example for control over overflow handling).

ROWSPAN, e.g. <TD ROWSPAN=2>

A positive integer value that defines how may rows this cell spans. The default ROWSPAN is 1. ROWSPAN=0 has a special significance and implies that the cell spans all rows from the current row up to the last row of the table.

COLSPAN, e.g. <TD COLSPAN=2>

A positive integer value that defines how may columns this cell spans. The default COLSPAN is 1. COLSPAN=0 has a special significance and implies that the cell spans all columns from the current column up to the last column of the table.

ALIGN, CHAR, CHAROFF and VALIGN

Specify values for horizontal and vertical alignment within table cells. See inheritance order of alignment properties.

Note: It is recommended that implementors provide support for the Netscape 1.1 WIDTH attribute for TH and TD, although this isn't part of the current specification. Document authors are advised to use the width attribute for the COL element instead.