The th element is a container for content that is rendered inside one cell of a table element in a format that distinguishes it as a header. Most browsers render the content as boldface. A cell is the intersection of a column and row. Other elements related to the th element are caption, col, colgroup, table, tbody, td, tfoot, thead, and tr. In addition to providing a wrapper for a cell's content, the th element defines a number of visible attributes that apply to a single cell, often overriding similar attributes set in lesser-nested elements in the table.

Four attributesabbr, axis, headers, and scopeare included in the HTML 4 specification in anticipation of nonvisual browsers that will use text-to-speech technology to describe content of an HTML pagea kind of "verbal rendering." Although these attributes are briefly described here for the sake of completeness, there is much more to their application in nonvisual browsers than is relevant in this book on Dynamic HTML. Consult the HTML 4 recommendation for more details.

Provides an abbreviated string that describes the cell's content. This is usually a brief label that a nonvisual browser would speak to describe what the value of the cell represents. The Properties choice for Netscape 6's context menu for this element displays a small window that includes an active link to the URL assigned to the attribute. Version 6 browsers provide no other functionality for this attribute.

Establishes the horizontal alignment characteristics of content within the cell covered by the th element.

Provides an abbreviated string that describes the cell's category. This is usually a brief label that a nonvisual browser would speak to describe what the value of the cell represents. The Properties choice for Netscape 6's context menu for this element displays a small window that includes an active link to the URL assigned to the attribute. Version 6 browsers provide no other functionality for this attribute.

Specifies an image file that is used as a backdrop to the cell. Unlike normal images that get loaded into browser content, a background image loads in its original size (without scaling) and tiles to fill the available cell space. Smaller images download faster but are obviously repeated more often in the background. Navigator 4, however, requires a minimum image size of 16 by 16 pixels. Animated GIFs are also allowable, but very distracting to the reader. When selecting a background image, be sure it is very muted in comparison to the main content so that the content stands out clearly. Background images, if used at all, should be extremely subtle.

Establishes a fill color (behind the text and other content) for the cell defined by the th element.

The colors used to render some of the pixels that create the illusion of borders around cells and the entire table. Internet Explorer applies the color to all four lines that make up the interior border of a cell. Therefore, colors of adjacent cells do not collide.

The 3-D effect of table borders in Internet Explorer is created by careful positioning of light and dark lines around the page's background or default color (see Figure 8-4 in the table element discussion). You can independently control the colors used for the dark and light lines by assigning values to the bordercolordark (left and top edges of the cell) and bordercolorlight (right and bottom edges) attributes.

Typically, you should assign complementary colors to the pair of attributes. There is also no rule that says you must assign a dark color to bordercolordark. The attributes merely control a well-defined set of lines so you can predict which lines of the border change with each attribute.

The char attribute defines the text character used as an alignment point for text within a cell. 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.

See charoff.

The colspan attribute specifies the number of columns across which the current table cell should extend itself. For each additional column included in the colspan count, one less th or td element is required for the table row. If you set the align attribute to center or right, the alignment is calculated on the full width of the th element across the specified number of columns. Unless the current cell is also specifies a rowspan attribute, the next table row returns to the original column count.

Used with IE data binding to associate a remote data source column name with the content of a table header cell. A datasrc (and optionally, a datapagesize) attribute must also be set for the enclosing table element. Works only with text file data sources in IE 5/Mac.

Points to one or more th or td elements that act as column or row headers for the current table cell. The assigned value is a space-delimited list of id attribute values that are assigned to the relevant th elements. A nonvisual browser could speak the cell's header before the content of the cell to help listeners identify the nature of the cell content. Although mainstream Version 6 browsers claim support for this attribute, neither have yet connected support for it.

The rectangular dimensions of a cell that may be different from the default size as calculated by the browser. When the values for these attributes are less than the minimum space required to render the table cell content, the browser overrides the attribute settings to make sure that all content appears, even if it means that text lines word-wrap. You can also stretch the dimensions of a table beyond the browser-calculated dimensions. Extra whitespace appears inside table cells to make up the difference. If you specify just one of these attributes, the browser performs all necessary calculations to automatically adjust the dimension along the other axis.

Due to the regular nature of tables, if you set a custom height for one cell in a row, the entire row is set to that height; similarly, setting the width of a cell causes the width of all cells in the column to be the same size.

Both the height and width attributes are deprecated in HTML 4 in favor of height and width style sheet attributes (which are not available for table cells in Navigator 4).

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.

The presence of the nowrap attribute instructs the browser to render the cell as wide as is necessary to display a line of nonbreaking text on one line. Abuse of this attribute can force the user into a great deal of inconvenient horizontal scrolling of the page to view all of the content. The nowrap attribute is deprecated in HTML 4. The nowrap attribute is deprecated in HTML 4 in favor of the white-space:nowrap CSS attribute and value.

The number of rows through which the current table cell should extend itself downward. For each additional row included in the rowspan count, one less th or td element is required for the next table row in that cell's position along the row.

The range of cells (relative to the current cell) that behave as though the current cell is the header for those cells. For tables whose structure is quite regular, the scope attribute is a simpler way of achieving what the headers attribute does, without having to define id attributes for the header cells. Although maintstream Version 6 browsers claim support for this attribute, neither have yet connected support for it.

Determines the vertical alignment of content within the td element. A value you set for an individual cell overrides the same attribute setting for outer containers, such as tr and tbody.

See height.