The rows and cols attributes

The <frameset> tag has one required attribute: either cols or rows--your choice. They define the size and number of columns (cols) or rows of either frames or nested framesets for the document window. Both attributes accept a quote-enclosed, comma-separated list of values that specify either the absolute (pixels) or relative (percentage or remaining space) width (for columns) or height (for rows) for the frames. The number of attribute values determines how many rows or columns of frames the browser will display in the document window.

As with tables, the browser will match the size you give a frameset as closely as possible. The browser will not, however, extend the boundaries of the main document window to accommodate framesets that would otherwise exceed those boundaries or fill the window with empty space if the specified frames don't fill the window. Rather, the browsers allocate space to a particular frame relative to all other frames in the row and column and resolutely fills the entire document window. (Did you notice a frame document window does not have scroll bars?)

For example,

<frameset rows="150,300,150">

creates three rows of frames, each extending across the entire document window. The first and last frames are set to 150 pixels tall, the second to 300 pixels. In reality, unless the browser window is exactly 600 pixels tall, the browser automatically and proportionately stretches or compresses the first and last frames so that each occupies one quarter of the window space. The center row occupies the remaining half of the window space.

Frame row and column size values expressed as a percentage of the window dimensions are more sensible. For instance, the following example is effectively identical to the previous one:

<frameset rows="25%,50%,25%">

Of course, if the percentages don't add up to 100 percent, the browser automatically and proportionally resizes each row to make up the difference.

If you are like us, making things add up is not a strength. Perhaps some of the frame designers suffer the same difficulty, which would explain why they included the very nifty asterisk option for <frameset> rows and cols values. It tells the browser to size the respective column or row to whatever space is left over after putting adjacent frames into the frameset.

For example, when the browser encounters the frame tag:

<frameset cols="100,*">

it makes a fixed-sized column 100 pixels wide, and then creates another frame column that occupies all of the remaining space in the frameset.

Here's a fancier layout example:

<frameset cols="10,*,10">

This one creates two very thin columns down the edges of the frameset and gives the remaining center portion to the middle column.

You may also use the asterisk for more than one row- or column-attribute value. In that case, the corresponding rows or columns equally divide the available space. For example,

<frameset rows="*,100,*">

creates a 100-pixel tall row in the middle of the frameset and equal-sized rows above and below it.

If you precede the asterisk with an integer value, the corresponding row or column gets proportionally more of the available space. For example,

<frameset cols="10%,3*,*,*">

creates four columns: the first column occupies 10 percent of the overall width of the frameset. The browser then gives the second three-fifths of the remaining space, and the third and the fourth are each given one-fifth of the remaining space.

Using asterisks (especially with the numeric prefix) makes it easy to divide up the remaining space in a frameset.

Be aware, too, that unless you explicitly tell it not to, the browser lets users manually resize the individual frame document's columns and rows, and hence change the relative proportions each frame occupies in their frames display. To prevent this, see the noresize attribute for the <frame> tag. [the section called "The <frame> Tag"]

Controlling frame borders and spacing

The lack of standards has given rise to a number of potentially conflicting attributes that you may use to define and change the borders surrounding the frames in a frameset.

Both Internet Explorer and Netscape use the frameborder attribute to disable or explicitly enable frame borders. (By default, every frame in a frameset as well as the frameset window itself is rendered with a 3D border; see Figure 12.1.) The two browsers' documentation disagree about the particular values for the frameborder attribute, but both acknowledge the other's conventions. Hence, setting the value of frameborder to 0 or no turns borders off (see Figure 12.2); 1 or yes turns borders on.

Internet Explorer and Netscape do disagree, however, as to how you may control the thickness of the borders. Internet Explorer supports the framespacing attribute, whose value is the number of pixels you want between frames (see Figure 12.2). The attribute affects all frames and framesets nested within the current frameset as displayed by Internet Explorer. In practice, you should set it once on the outermost <frameset> to create a consistent border appearance for all of the frames in a single page.

Netscape only accepts the border attribute to define the border width, with an integer value in pixels. Like Internet Explorer, Netscape allows you to include the frameborder attribute with any <frameset> tag, affecting all nested frames and framesets, but unlike Internet Explorer, Netscape restricts the border attribute to the outermost <frameset>, ensuring that all frame borders are the same width within that <frameset>.

Since browsers ignore unsupported attributes, it is possible to define frame borders so that both browsers do the right thing. Just make sure to use the same framespacing and border values.

Finally, with Netscape you can control the color of the frame borders using the bordercolor attribute (Figure 12.3). It accepts a color name or hexadecimal triple as its value. A complete list of color names and values can be found in Appendix F, Color Names and Values.

Frames and JavaScript

Internet Explorer and Netscape support JavaScript-related event handlers that let your frame documents react when they are first loaded and when the frame window gets resized (onLoad); unloaded from the browser by the user (onUnload); when the window containing the frameset loses focus, such as when the user selects another window (onBlur); or when the frameset becomes the active window (onFocus). Included as <frameset> attributes, these event handlers take quote-enclosed lists of JavaScript commands and function calls as their value. For example, you might notify the user when all the contents have been loaded into their respective frames of a lengthy frameset:

<frameset onLoad="window.alert('Everything is loaded. You may now continue.')">

These four attributes may also be used with the <body> tag. We cover JavaScript in more detail in 13.3.3.