Bug#637249: document undocumented prejudice against experimental
One thought one could comment out
//APT::Default-Release "experimental"; //instead just list it first in sources.list
but in fact the "cards are still stacked" against experimental.
There is some behinds the scenes _undocumented built in prejudice_
apt-config dump doesn't show it.
man apt_preferences says a tiny bit
to the versions coming from archives which in their Release files
are marked as "NotAutomatic: yes" but not as "ButAutomaticUpgrades:
yes" like the debian experimental archive.