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entire image need not be covered with sensitive regions: if the passed
coordinates don't fall within a specified shape, the default document
gets sent back to the browser.
This is just one example of how an image map may be processed and
the accessory files required for that process. Please huddle with your
webmaster and server manuals to discover how to implement a server-
side image map for your own documents and system.
6.5.2. Client-Side Image Maps
The obvious downside to server-side image maps is that they require
a server. That means you need access to the required HTTP server or
its /cgi-bin directory, either of which is rarely available to anyone oth-
er than owners or system administrators. And server-side image maps
limit portability because not all image-map processing applications are
the same.
Server-side image maps also mean delays for the user while browsing
because the browser must get the server's attention to process the im-
age coordinates. This is true even if there's no action to take, such as
when the user clicks on a section of the image that isn't hyperlinked and
doesn't lead anywhere.
Client-side image maps suffer from none of these difficulties. Enabled
by the usemap attribute for the <img> tag and defined by special <map>
and <area> extension tags, client-side image maps let authors include
in their documents coordinates and links that describe the sensitive re-
gions of an image. The browser on the client computer translates the
coordinates of the mouse position within the image into an action, such
as loading and displaying another document. And special JavaScript-en-
abled attributes provide a wealth of special effects for client-side image
maps. [ JavaScript Event Handlers, 12.3.3 ]
To create a client-side image map, include the usemap attribute as part
of the <img> tag. [*] Its value is the URL of a <map> segment in an HTML
document that contains the map coordinates and related link URLs. The
document in the URL identifies the HTML or XHTML document contain-
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