@MaxStirner: Because that's much better than letting a random package fill up your drive and screw everything up.
The high mark is based on the largest packages shipped (USBNet or Python, depending on the platform).
MRPI itself will enforce it
c.f.,
http://trac.ak-team.com/trac/browser...taller.sh#L328
Some packages may also enforce a stricter one if need be in their own install script (Python does:
http://trac.ak-team.com/trac/browser...install.sh#L50).
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KPVBooklet itself may appear to behave, but expect all kinds of weird quirks inside KOReader itself when started by KPVBooklet.