[texhax] The At and the Asterisk in LaTeX

[P. R. Stanley]

Hi folks
1. What is the general significance of the asterisk "*" in LaTeX and 
in particular, the xy package? I see it used in (0, 0))*{}, **\dir or 
**\crv{}. Is it more than syntax sugar?
2. What about the "@" symbol?
I've no problem memorising the commands though it'd be helpful to 
know what each part means.
Thanks in advance for your help.
Cheers
Paul