Auto-complete command line arguments

Question

In bash, executables such as mplayer and imagemagick\'s \"convert\" have a cool auto-complete functionality on their command line arguments. For instance, if I type

Answer 1

This is an example of BASH's smart completion. A basic description is here, a guide to writing your own extensions is here and another (Debian-based) guide is here. And here's a fuller featured introduction to the complete command (the command that facilitates this behaviour).