[Xcb] Why are predefined atoms not static constants?

[Ulrich Eckhardt]

Hi!

I'm looking at xcb_atom.h, where I find e.g. 

   extern const xcb_atom_t PRIMARY;

What I'm wondering is why this isn't simply

   static const xcb_atom_t PRIMARY = ...

I know, there are a bunch of reasons for either variant, I just wanted to ask 
which of them were the reasons for doing things this way here. Can anyone 
enlighten me?

Cheers!

Uli