Benefits
Opera displays the acronym title as a tooltip.
Mozilla goes even further, automatically rendering acronyms with a dotted underline.
You can override this default behavior with cascading style sheets, or use CSS to get a similar effect in other browsers.
Google benefits. Google indexes the acronym title as well as the acronym itself, so people can find your site whether they search for the acronym or the spelled−out description.
How to do it
<acronym title="cascading style sheets">CSS</acronym>
<acronym lang="en" title="cascading style sheets">CSS</acronym>
<span lang="en">CSS</span>
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