Completion Widget Example
=========================
The first step is to define the widget:
zle -C complete complete-word complete-files
Then the widget can be bound to a key using the bindkey builtin command:
bindkey '^X\t' complete
After that the shell function complete-files will be invoked after
typing control-X and TAB. The function should then generate the
matches, e.g.:
complete-files () { compadd - * }
This function will complete files in the current directory matching the
current word.