Understanding rebase

What properties must commits have for them to be rebase-able?

One example arrangement that would cause a rebase to fail is:

- change lines 10, 12, 14 in branch A
- change lines 11, 13, 15 in branch B

These changes are commutative (I believe), but that is insufficient for avoiding conflicts on a rebaes. For a concrete example of this, see:

http://assorted.svn.sourceforge.net/viewvc/assorted/sandbox/trunk/src/git/gitsvn.bash?revision=1065&view=markup

Another question that probably gets at the same thing: I understand what rebasing gives me from a high level (rearranging a branch of commits to be in a series with another branch), but is there a simple explanation of how, precisely, this is accomplished?

Thanks in advance!