Yasnippet tries functions in
yas/prompt-functions when it needs user to
select one choice, such as selecting snippets with the same trigger key, such
as helper method
popup is a visual popup interface library extracted from auto-complete
by its author. It has better look and feel than all the built-in
yas/prompt-functions. Also it is easy to customize, and its isearch mode is
very efficient, the items are filtered on-the-fly when typing.