Tab inserts spaces instead of complete by default

[Sébastien Pierre <sebastien.pierre@xxxxxxxxx>]

Hi all,

I've recently switched to Zsh and am currently trying to make the "tab"
completion work as in bash/tcsh. If I start a new zsh shell, and I hit the
"tab" key, a tab is inserted in the command line, instead of showing the
possible completions -- when I type something, completion happens as
expected.

So my question is: how can I configure zsh to always show possible
completions, even when there is no character on the prompt ?

 -- Sébastien