expand and contract shortened URLs - a search.twitter.com feature

For Firefox and Flock, using the LongURL Mobile Expander Add-on enables the user to see what the short URL expands to, but Safari search.twitter.com has this feature built-in...

• When Safari search.twitter.com encounters a shortened URL, is added next to the short URL. Click to expand the shortened URL, and click to restore to the short URL.

NOTE: I have not found this feature in the Safari documentation yet. Any know where this feature is documented?

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