/usr/share/doc/debian-installer/devel/available-hooks.txt is in debian-installer 20101020ubuntu318.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | The overview of the currently assigned menu-item numbers has been moved to
the "D-I Internals" document.
See installer/doc/devel/internals/available-hooks.xml, or
http://d-i.alioth.debian.org/doc/internals/.
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