The realization of the pop-up window that [vim plug-in development] completes automatically?

  question, vim

图片描述

Need to write a plug-in, there is a function is to press a set of shortcuts pop-up window as shown in the figure, this to call vim that function? Or by what means?

Looking at vim built-in functions, there is no such thing for interactive classes.

Ask the great god for help.

:help completion-functions