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6.6. Creating Searchable Documents

Another extensible form of an HTML link that does not use the <a> tag is one that causes the server to search a database for a document that contains a user-specified keyword or words. An HTML document that contains such a link is known as a searchable document.

6.6.1. The <isindex> Tag (Deprecated)

No longer supported in the HTML 4 or XHTML standards, authors at one time used the <isindex> tag to pass keywords along with a search-engine's URL to the server. The server then matched the keywords against a database of terms to select the next document for display. Today's authors mostly use forms to pass information to the server and supporting programs. See Chapter 9, "Forms" for details.

<isindex>

Function:

Indicates that a document can be searched

Attributes:

ACTION

LANG

CLASS

PROMPT

DIR

STYLE

ID

TITLE

End tag:

None in HTML; </isindex> or <isindex ... /> with XHTML

Contains:

Nothing

Used in:

head_content

When a browser encounters the <isindex> tag, it adds a standard search interface to the document (rendered by Internet Explorer in Figure 6-8):

<html>
<head>
<title>Kumquat Advice Database</title>
<base href="cgi-bin/quat-query">
<isindex>
</head>
<body>
<h3>Kumquat Advice Database</h3>
<p>
Search this database to learn more about kumquats!
</body>
</html>

The user types a list of space-separated keywords into the field provided. When the user presses the Enter key, the browser automatically appends the query list to the end of a URL and passes the information to the server for further processing.

While the HTML and XHTML standards only allow the deprecated <isindex> tag to be placed in the document header, most browsers let the tag appear anywhere in the document and insert the search field in the content flow where the <isindex> tag appears. This convenient extension lets you add instructions and other useful elements before presenting the user with the actual search field.

Figure 6-8

Figure 6-8. A searchable document

6.6.1.1. The prompt attribute

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

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.

6.6.1.2. The query URL

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


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