6:755d1e0d79e9 
5:9ce2ce29723a 3:a3e00c7dbf11 4:bb4475edb621 
4:bb4475edb621 1:5d953a1917d1 
3:a3e00c7dbf11 
2:befc7d89d081 
1:5d953a1917d1 
0:837088b6e1d9 

should work with tag/branch/node/rev
tip^: 5
default^: 5
755d1e0d79e9^: 5
6^: 5

some random lookups
6^^: 3
6^^^: 2
6^^^^: 1
6^^^^^: 0
6^^^^^^: -1
6^1: 5
6^2: abort: unknown revision '6^2'!
6^^2: 4
6^1^2: 4
6^^3: abort: unknown revision '6^^3'!
6~: abort: unknown revision '6~'!
6~1: 5
6~2: 3
6~3: 2
6~4: 1
6~5: 0
6~42: -1
6~1^2: 4
6~1^2~2: 0

with a tag "6^" pointing to rev 1
6^: 1
6^1: 5
6~1: 5
6^^: 3

with a tag "foo^bar" pointing to rev 2
foo^bar: 2
foo^bar^: abort: unknown revision 'foo^bar^'!