Documentation/config/sequencer.txt

   1 sequence.editor::
   2         Text editor used by `git rebase -i` for editing the rebase instruction file.
   3         The value is meant to be interpreted by the shell when it is used.
   4         It can be overridden by the `GIT_SEQUENCE_EDITOR` environment variable.
   5         When not configured the default commit message editor is used instead.