This might not be new but I haven't seen it before. If you come across a page that doesn't exist on www.invms.co.uk it will show you a nice error page like so many other websites do, except that the IMS 404 error page is a bit more advanced. First of all it deconstructs the requested path and prepares that for a site search. This "suggest searchterm" is then also used to make an AJAX search (using tw-sack) asyncronously inside the browser but then only on the title of the various pages it can find.
The advantage of doing an AJAX search instead of a server-side search is that the page loads faster. First it loads the important message ("Page not found"), then as an added bonus it shows some additional help. It also means that all those portscanners and other phishers (who don't use webbrowsers to do their scanning) don't cause lots of excessive searches on the server.
To test this, go to a page that doesn't exist like http://www.invms.co.uk/Literature/foobar or http://www.invms.co.uk/IMS-Select-Funds/IMS-Select-Income-FundXXXFollow @peterbe on Twitter