There is also a dropped plugin of Bootstrap 2 which is still available in Ace admin template.
It's typeahead plugin and is used by Tag input plugin and search box demo.
For more info about it, please see:
http://getbootstrap.com/2.3.2/javascript.html#typeahead
To avoid conflicts with the new Typeahead.js plugin, its been renamed to bs_typeahead.
Of course the plugins have methods to resolve conflicts by calling $.fn.typeahead.noConflict(); but I found it easier to rename it to something else especially when using both plugins inside an ajax page and coming back and forth to that page multiple times!

It's the updated version of Bootstrap Typeahead with more features.
For more info and documentation about it, please see its page at:
https://twitter.github.io/typeahead.js/
To use it, you should include:
components/typeahead.js/dist/typeahead.jquery.js

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