The browser provides a leading prompt just above or to the left of the user-entry field. Internet Explorer's default prompt, for example, is "You can search this index. Type the keyword(s) you want to search for:" (Figure 6-8). That default prompt is not the best for all occasions, so it is possible to change it with the prompt attribute.

When added to the <isindex> tag, the value of the prompt attribute is the string of text that precedes the keyword entry field placed in the document by the browser.

For example, compare Figure 6-8 with Figure 6-9, in which we added the following prompt to the previous source example:

<isindex prompt="To learn more about kumquats, enter a keyword:">

Figure 6-9. The prompt attribute creates custom prompts in searchable documents

Older browsers will ignore the prompt attribute, but there is little reason not to include a better prompt string for your more up-to-date readership.

Besides the <isindex> tag in the header of a searchable document, the other important element of this special tag is the query URL. By default, it is the URL of the source document itself -- not good if your document can't handle the query. Rather, most authors use the <base> attribute to point to a different URL for the search. Section 6.7.1, "The <base> Header Element"

The browser appends a question mark to the query URL, followed by the specified search parameters. Nonprintable characters are appropriately encoded; multiple parameters are separated by a plus sign (+).

In the previous example, if a user types "insect control" in the search field, the browser would retrieve the URL:

cgi-bin/quat-query?insect+control

For Internet Explorer only, you can specify the query URL for the index with the action attribute. The effect is exactly as if you had used the href attribute with the <base> tag: the browser links to the specified URL with the search parameters appended to the URL.

The class and style attributes allow you to supply display properties and class names to control the appearance of the tag, although their value seems limited for <isindex>. The id and title attributes allow you to create a name and title for the tag; the name might referenced by a hyperlink. Section 4.1.1.4, "The id attribute" Section 4.1.1.5, "The title attribute" Section 8.1.1, "Inline Styles: The style Attribute" Section 8.3, "Style Classes"

The dir and lang attributes define the language used for this tag and the direction in which text is rendered. Again, their use is not apparent with <isindex>. Section 3.6.1.1, "The dir attribute" Section 3.6.1.2, "The lang attribute"

Like image maps, searchable documents require support from the server to make things work. How the server interprets the query URL and its parameters is not defined by the HTML or XHTML standards.

You should consult your server's documentation to determine how you can receive and use the search parameters to locate the desired document. Typically, the server breaks the parameters out of the query URL and passes them to a program designated by the URL.