Note that commands that operate on the history of the current branch(e.g. git commit to build a new history on top of it) still workwhile the HEAD is detached. They update the HEAD to point at the tipof the updated history without affecting any branch. Commands thatupdate or inquire information about the current branch (e.g. gitbranch --set-upstream-to that sets what remote-tracking branch thecurrent branch integrates with) obviously do not work, as there is no(real) current branch to ask about in this state.