Invariant sections? GFPL

[Clytie Siddall <clytie riverland net au>]

Hello all :)

I'm taking my first stumbles into documentation translation, and I've  
started with Bug-Buddy, since I know people in my community have  
difficulty reporting bugs due to lack of translated material, and  
this will make the translated application easier to use. The POT for  
the bug-buddy doc. is neatly packaged on the modules page [1], and  
away I go...

However, my first contact with the GFPL has confused me a tad. I  
don't understand the function of the phrase "Invariant Sections" in  
this part of the copyright string:
__________________________
Permission is granted to copy, distribute and/or modify this document  
under the terms of the GNU Free Documentation License (GFDL), Version  
1.1 or any later version published by the Free Software Foundation  
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover  
Texts. You can find a copy of the GFDL..."
__________________________
Now, invariant sections are sections which don't change. Why would  
these be prohibited? Would not changing information included in the  
licence be more of a concern? (Also, why are these terms capitalized?)

Thankyou for any help you can offer on this. I am probably missing  
something here (again ;) ).

from Clytie (vi-VN, Vietnamese free-software translation team / nhÃm  
Viát hÃa phán mám tá do)
http://groups-beta.google.com/group/vi-VN

[1] http://kvota.net/doc-l10n/by-modules.html