[emmelaich]

A branch is just a series of commits; if any one of the commits has a different hash (as this hack will do) then the commit and all following commits will have a different hash.

Including the id of the branch (the HEAD).

[tsm]

It's simpler than that: a branch is just a pointer to one specific commit (with a specific SHA)

[emmelaich]

True, but it's both.

Just as a link in a linked list is often the list and the node in the list.