Links and Webs - HTML and XHTML: The Definitive Guide - page 349

6.5.4.4. The nohref attribute
The nohref attribute for the <area> tag defines a mouse-sensitive region
in a client-side image map for which no action is taken, even though the
user may select it. You must include either an href or a nohref attribute
for each <area> tag.
6.5.4.5. The notab, taborder, and tabindex attributes
As an alternative to the mouse, a user may choose a document "hot-
spot," such as a hyperlink embedded in an image map, by pressing the
Tab key. Once the user chooses the hotspot, he activates the hyperlink
by pressing the Enter key. By default, the browser steps to each hot-
spot in the order in which they appear in the document. You can now
change that default order with what was originally introduced by Inter-
net Explorer with the taborder attribute and is now standardized as the
tabindex attribute. The value of the attribute is an integer indicating the
position of this area in the overall tab sequence for the document.
Supported by Internet Explorer only and not part of the HTML 4 and
XHTML standards, notab areas get passed over as the user presses the
Tab key to move the cursor around the document. Otherwise, this area
will be part of the tabbing sequence. The attribute is useful, of course,
in combination with the nohref attribute.
Internet Explorer version 4 supported the notab and taborder attributes.
Versions 5 and later support tabindex , too, so use the standard rather
than the extension attributes.
6.5.4.6. The event attributes
The same mouse-related JavaScript event handlers that work for the
anchor ( <a> ) tag also work with client-side image-map hyperlinks. The
value of the event handler isenclosed in quotation marksone or a se-
quence of semicolon-separated JavaScript expressions, methods, and