An Introduction to HTML Tables

Table start with an optional caption followed one or more rows. Each row is formed by one or more cells, which are differentiated into header and data cells. Cells can be merged across rows and columns, and include attributes assisting rendering to speech and braille, or for exporting table data into databases. The model provides little direct support for control over appearence, for example border styles and margins, as these can be handled via subclassing and associated style sheets.

Tables can contain a wide range of content, such as headers, lists, paragraphs, forms, figures, preformatted text and even nested tables. When the table is flush left or right, subsequent elements will be flowed around the table if there is sufficient room. This behaviour is disabled when the noflow attribute is given or the table align attribute is center (the default), or justify.

Example

<TABLE BORDER=ALL>
  <CAPTION>A test table with merged cells</CAPTION>
  <TR><TH ROWSPAN=2><TH COLSPAN=2>Average
      <TH ROWSPAN=2>other<BR>category<TH>Misc
  <TR><TH>height<TH>weight
  <TR><TH ALIGN=LEFT>males<TD>1.9<TD>0.003
  <TR><TH ALIGN=LEFT ROWSPAN=2>females<TD>1.7<TD>0.002
</TABLE>

This would be rendered something like:

              A test table with merged cells
    /--------------------------------------------------\
    |          |      Average      |  other   |  Misc  |
    |          |-------------------| category |--------|
    |          |  height |  weight |          |        |
    |-----------------------------------------|--------|
    | males    |   1.9   |  0.003  |          |        |
    |-----------------------------------------|--------|
    | females  |   1.7   |  0.002  |          |        |
    \--------------------------------------------------/

There are several points to note:

• By default, header cells are centered while data cells are flush left. This can be overriden by the ALIGN attribute for the cell or a matching HSPEC element.
• Cells 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).
• 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 handside of the table, and rendered as empty cells.
• The row count is determined by the TR elements - any rows implied by cells spanning rows beyond this should be ignored.
• The user agent should be able to recover from a missing <TR> tag prior to the first row as the TH and TD elements can only occur within the TR element.
• It is invalid to have cells overlap, see below for an example. In such cases, the rendering is implementation dependent.

An example of an invalid table:

<table border=all>
<tr><td rowspan=2>1<td>2<td>3<td>4<td>5
<tr><td rowspan=2>6
<tr><td colspan=2>7<td>8
</table>

which looks something like:

    /-------------------\
    | 1 | 2 | 3 | 4 | 5 |
    |   |---------------|
    |   | 6 |   |   |   |    The cells labelled 6 and 7 overlap!
    |---|...|-----------|
    | 7 :   | 8 |   |   |
    \-------------------/