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.

The first one uses a list of well known keywords and provides a hint based on that and goes by the name Function Completion. It is triggered by selecting Edit->Auto-Completion->Function Completion or automatically when a certain amount of characters is typed (see also Preferences).
The second one retrieves all the words from the current file and provides hinting on that, named Word Completion. This is triggered by selecting Edit->Auto-Completion->Word Completion, or by entering a set number of characters (again, see Preferences). Word completion is the only type that can automatically finish a word without displaying a list of options first.

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 XML files and how to make your own ones, please refer to NpWiki++.