Auto completion

Notepad++ has autocompletion capabilities, allowing it to finish a word that you are typing by giving a list of possible options, or immediately inserting it when only one possibility is left (powered by the Scintilla component).

There are two types of auto completion. 

Somewhat related but not exactly the same is the display of function parameter hints, or calltips. This is a small tooltip that will show the required parameters (and possibly some details of them) for a function a call to which is being edited. This is specifically targeted for programming purposes and serves no real value for other tasks. The calltip will highlight the current parameter being edited for a quick emphasis on what is actually needed. It is purely passive and will not modify the text in any way. To trigger a calltip (if one can be found), select Edit->Auto-Completion->Function parameters hint.

Autocompletion is language based (see Languages) and has different API files for each language. For more details on these API files and how to make your own, refer to
http://apps.sourceforge.net/mediawiki/notepad-plus/index.php?title=Auto Completion