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13.4. Affecting Table Appearance

The HTML table standard provides many tags for controlling the display of tables. Bear in mind that, as with most formatting tags, browsers have their own way of interpreting your instructions, so results may vary among browser releases and platforms. This is particularly true of tables since the standard is still being nailed down. As always, it is best to test in a variety of viewing environments.

It is important to note that some of the attributes that affect appearance (align, valign, and bgcolor) have been deprecated by the HTML 4.01 specification in favor of achieving the same effects with style sheets. Expect the major browsers, however, to continue supporting the following methods until style sheets are universally supported.

13.4.1. Borders, Frames, and Rules

The traditional method for adding a border around a table is the border attribute, which affects the display of the borders around and within the table. For more finely tuned control, the HTML separates control over the outer edge of the table (its frame) from the lines between cells within the table (rules). Let's look at all three attributes.

13.4.3. Aligning Text in Cells

By default, the text (or any element) in a data cell (<td>) is positioned flush left and centered vertically within the available height of the cell, as shown in Figure 13-7.

Figure 13-7

Figure 13-7. Default placement of data within a cell

Table header text (<th>) is generally displayed in bold text centered horizontally and vertically in the cell. You can override these defaults using the align and valign attributes at either the row or cell level.

Row Settings

Alignment settings specified within the <tr> tag affect all the table cells (<td> or <th>) within that row. This makes it easy to apply alignment changes across multiple cells.

Cell Settings

Alignment attributes within a cell (<td> or <th>) apply to the current cell. Cell settings override row settings. Furthermore, alignment settings within the contents of the cell (e.g., <p align=right>) take precedence over both cell and row settings.

Horizontal alignment is specified with the align attribute, which takes the standardleft, right, or center values. These values work the same as regular paragraph alignment. (The align attribute has been deprecated in favor of style sheet controls.)

Vertical alignment is controlled using the valign attribute, which can be set to top, middle (the default), bottom, or baseline ("first text line appears on a baseline common to all the cells in the row," but this setting is not as well supported).

By default, the text in a cell automatically wraps to fill the allotted space. There is a nowrap attribute which can be added within the table cell (<td> or <th>) to keep text on one line (unless broken by a <br> or <p>). Unfortunately, most browsers (except IE 5 and higher) ignore the attribute and wrap the text anyway. When nowrap is supported, the table cell resizes wider if it needs to accommodate the line of text.

13.4.4. Sizing Tables

You can control the size of the entire table as well as the size of rows and columns. By default, a table (and its rows and columns) are sized automatically to the minimum dimensions required to fit their contents. In many cases, it is desirable to assign a table or column a specific size (especially when using the table to build a page structure).

If the contents require a width greater than the specified size, the table generally resizes to accommodate the contents. Size specifications are treated as suggestions that will be followed as long as they don't conflict with other display directions. In effect, by specifying the size of a table you are merely specifying the minimum size. It is best to specify ample room to accommodate the contents of the cells.

13.4.5. Table Cell Spacing

There are two types of space that can be added in and around table cells: cell padding and cell spacing. The cellpadding and cellspacing attributes are used within the <table> tag and apply to the whole table (you can't specify padding or spacing for individual cells).

cellspacing

The amount of space between table cells is controlled by the cellspacing attribute within the <table> tag. Values are specified in number of pixels. Increasing the cell spacing results in wider shaded borders between cells. In the left image in Figure 13-8, the gray areas indicate the 10 pixels of cell spacing added between cells. The default value for cellspacing is 2; therefore, if no cellspacing is specified, browsers will automatically place 2 pixels of space between cells.

Figure 13-8

Figure 13-8. Cell spacing versus cell padding

cellpadding

Cell padding refers to the amount of space between the cell's border and the contents of the cell (as indicated in Figure 13-8). It is specified using the cellpadding attribute within the <table> tag. Values are specified in number of pixels; the default value is 1. Relative values (percentages of available space) may also be used.

Different effects can be created using different combinations of spacing and padding. If you want your table to be seamless, as when it is holding together an image, be sure to set the border, cellspacing, and cellpadding to 0, as follows:

<TABLE BORDER=0 CELLPADDING=0 CELLSPACING=0>

13.4.6. Coloring Tables

You can specify a background color for the entire table (<table>), for selected rows (<tr>), or for individual cells (<td> or <th>) by placing the bgcolor attribute in the appropriate tag. The bgcolor attribute is recognized by Internet Explorer Versions 2.0 and higher and Navigator Versions 3.0 and higher.

Color values can be specified by either their hexadecimal RGB values or a standard color name. For more information on specifying color in HTML, see Chapter 16, "Specifying Color in HTML".

Color settings in a cell override settings made at the row level, which override settings made at the table level. To illustrate, in the following example, the whole table is set to light gray, the second row is set to medium gray, and the furthest right cell in that row is set to dark gray. Figure 13-9 shows the results.

<TABLE BORDER=1 BGCOLOR="#CCCCCC">
<TR>
<TD></TD><TD></TD><TD></TD>
</TR>
<TR BGCOLOR="#999999">
<TD></TD><TD></TD><TD BGCOLOR="#333333"></TD>
</TR>
<TR>
<TD></TD><TD></TD><TD></TD>
</TR>
<TR>
<TD></TD><TD></TD><TD></TD>
</TR>
</TABLE>
Figure 13-9

Figure 13-9. Effects of setting background colors at cell, row, and table levels

Navigator and Internet Explorer treat background colors at the table level differently. Navigator fills every cell in the table with the specified color, but the border picks up the color of the document background. IE fills the entire table area, including the borders, with the specified color for a more unified effect. When you set background colors for individual cells or rows, it will be displayed the same way on both browsers (although Navigator uses the document background color for empty cells).



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