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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)
Before it was deprecated in
both the HTML 4 and XHTML standards, authors used to use 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 for details.
<isindex>Function Indicates that a document can be searched Attributes action (  ),class, dir, id, lang, prompt, style, title End tag None in HTML; </isindex> or <isindex ... /> in XHTML Contains Nothing Used in head_content |
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=">
<isindex>
</head>
<body>
<h3>Kumquat Advice Database</h3>
<p>
Search this database to learn more about kumquats!
</body>
</html>
Figure 6-8. A searchable document
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 allow the deprecated
<isindex> tag to be placed only 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.
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 has even changed over the years. Version 5, for
example, used "This is a searchable index. Enter
search keywords:". Version 6's
prompt is shown in 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 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. [<base>]
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 plus
signs (+).
In the previous example, if a user typed "insect
control" in the search field, the browser would
retrieve the URL:
?insect+control
6.6.1.3 The action attribute
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.
While the action attribute provides the desirable
feature of divorcing the document's base URL from
the search index URL, it will cause your searches to fail if the user
is not using Internet Explorer. For this reason, we do not recommend
that you use the action attribute to specify the
query URL for the search.
6.6.1.4 The class, dir, id, lang, style, and title attributes
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 be referenced by a hyperlink. [Section 4.1.1.4] [Section 4.1.1.4] [Section 8.1.1] [Section 8.3]
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]
[Section 3.6.1.2]
6.6.1.5 Server dependencies
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.
