From W3C Wiki

Contents 1 <colgroup> 1.1 Point 1.2 HTML Attributes 1.3 Examples 1.3.1 Example A 1.4 HTML Reference

<colgroup>

The <colgroup> element represents a group of one or more columns in the table that is its parent.

Point

• As a child of a table element, after any caption elements and before any thead, tbody, tfoot, and tr elements.
• If the colgroup element contains no col elements, then the element may have a span content attribute specified. [Example A]

HTML Attributes

• span = valid non-negative integer

See also global attributes, but note that the style attribute is crippled: you can only control the following:

• background-color
• border
• width
• visibility

Examples

Example A

[try it]:

<table>
  <colgroup span="2" style="background-color: #ff0000;"></colgroup>
  <tr>
    <td>1</td>
    <td>2</td>
    <td>3</td>
  </tr>
  <tr>
    <td>4</td>
    <td>5</td>
    <td>6</td>
  </tr>  
</table>

HTML Reference

The HTML5 specification defines the <colgroup> element in 4.9.3 The colgroup element.