Double Colon in $PATH

[Julius Plenz <julius@xxxxxxxxx>]

Hi!

I recently discovered (rather by accident, though) that a double-colon
in the PATH variable is treated by Zsh (Ash and Bash, too) as if there was
".", the current directory, in the PATH variable.

Example:

prompt> echo $PATH && pwd
::
/bin
prompt> ls
[directory listing of /bin]

Now this is really confusing me. I've already asked several people,
and neither one of them could tell my why Zsh (and other shells) do
this. I'd appreciate it very much if any of you guys could give me a
hint or explain this behaviour to me.

Thank you!

Julius