What are the official source file indentation standards?

[Sidney Markowitz]

Can someone tell me or point me to the indentation standards for the 
perl source files in SpamAssassin? Use tab characters, or only spaces, 
or it doesn't matter? If tabs are used what tab width? And indent by how 
much? I'm having difficulty distinguishing standards from what may be 
mistakes or simply lack of standards in some source files.

If any of you use emacs and have set up the right options in their 
~/.emacs file for perl-mode, seeing what they are would make it easy for me.

Thanks,
 -- sidney