The colgroup element provides shortcuts to assigning widths and other characteristics (styles) to one or more subsets of columns within a table. With this information appearing early in the table element source code, a browser equipped to do so starts rendering the table before all source code for the table has loaded (at which time it would otherwise perform all of its geographical calculations).

You can use the colgroup element in combination with the col element or by itself. You may also define a colgroup that has col elements nested within to assist in defining subsets of columns that share some attribute or style settings. The need for the element's end tag is determined by the presence of standalone col elements following the colgroup element. For example, if you specify column groupings entirely with colgroup elements, end tags are not necessary:

If you have a freestanding col element following the colgroup element, you must clearly end the colgroup element before the standalone col element:

The structure depends on how you need to assign widths and styles to individual columns or contiguous columns. To create a column grouping that consists of multiple adjacent columns, use the span attribute. This is entirely different from the colspan attribute of a td element, which has the visual impact of joining adjacent cells together as one. The span attribute helps define the number of columns to be treated structurally as a group (for assigning attribute and style sheet settings across multiple columns, regardless of the column content).

No matter how you address the column structure of your table, the total number of columns defined in all col and colgroup elements should equal the physical number of columns you intend for the table. The following three skeletal examples specify HTML 4 tables with six columns:

HTML 4 specifications for the colgroup element exceed the implementation in IE for Windows and Navigator through Version 6. For example, HTML 4 provides for alignment within a column to be around any character, such as the decimal point of a money amount. This kind of feature adds to the rationale behind the col element (see the col element for an example).

Syntactically, there is little difference between a colgroup and col element. A colgroup element, however, lends a structural integrity to a group of columns that is rendered differently when the containing table element specifies rules="groups"; the browser draws rule lines (standard table borders in IE) only between colgroup elements, and not col elements.

Support indicated here for Netscape 6 is based on the browser's DOM implementation. The DOM reports to scripts that the colgroup element and its attributes exist (reflected as properties). But as of Netscape 7, the element does not perform its intended tasks. A later version will likely connect the element's internal wiring.

Establishes the horizontal alignment characteristics of content within column(s) covered by the colgroup element. The HTML 4 specification defines settings for the align attribute that are not yet reflected in the CSS specification. For example, there is no CSS equivalent for the alignment by character. See the colgroup element description about Netscape 6 compatibility.

The char attribute defines the text character used as an alignment point for text within a column. This attribute is of value only for the align attribute set to "char". Microsoft documents a ch attribute, which corresponds to the standards-based char attribute. In any case, the browser does not respond to either attribute. Netscape 7 has not yet connected support for the char attribute.

The charoff attribute lets you set a specific offset point at which the character specified by the char attribute is to appear within a cell. This attribute is provided in case the browser default positioning does not meet with the design goals of the table. Microsoft documents a choff attribute, which corresponds to the standards-based charoff attribute. In any case, the browser does not respond to either attribute. Netscape 7 has not yet connected support for the charoff attribute.

The language being used for the element's attribute values and content. A browser can use this information to assist in proper rendering of content with respect to details such as treatment of ligatures (when supported by a particular font or required by a written language), quotation marks, and hyphenation. Other applications and search engines might use this information to aid the selection of spell-checking dictionaries and the creation of indices.

Defines the number of adjacent columns for which the colgroup element's attribute and style settings apply. If this attribute is missing, the colgroup element governs a single column. You can combine multiple colgroup elements of different span sizes as needed for your column subgrouping. See the colgroup element description about Netscape 6 compatibility.

Determines the vertical alignment of content within cells of the column(s) covered by the colgroup element. You can override the vertical alignment for a particular cell anywhere in the column. See the colgroup element description about Netscape 6 compatibility.

Defines the maximum width for the column(s) covered by the colgroup element. In practice (in IE 4 and later for Windows, anyway), the browser won't render a column narrower than the widest contiguous stretch of characters not containing whitespace (e.g., the longest word). The precise measure of such a column width, of course, depends on the font characteristics of the content, as well. See the colgroup element description about Netscape 6 compatibility.