Whilst working on a recent demonstration I spotted this peculiar behaviour in all versions of Internet Explorer.
If you have a link which has a png background image and you use the Microsoft AlphaImageLoader to make it render with alpha transparency then ONLY the parts of the image that do not have 'transparency' are clickable.
Although this is restricted to only Internet Explorer I thought that it might be useful, so have this demo to show the effect.
It could be used for irregular shaped image maps.
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