docs: def is_feature_branch(self, branch_name):
          """
          Try to determine whether a branch name refers to a feature branch.
  
          :param branch_name: The name of a branch (a string).
          :returns: :data:`True` if the branch name appears to refer to a feature
                    branch, :data:`False` otherwise.
  
          This method is used by :func:`merge_up()` to determine whether the
          feature branch that was merged should be deleted or closed.
  
          If the branch name matches :attr:`default_revision` or one of the
          branch names of the :attr:`releases` then it is not considered a
          feature branch, which means it won't be closed.
          """
          # The following checks are intentionally ordered from lightweight to heavyweight.
          if branch_name == self.default_revision:
              # The default branch is never a feature branch.
              return False
          elif branch_name not in self.branches:
              # Invalid branch names can't be feature branch names.
              return False
          elif self.release_scheme == 'branches' and branch_name in self.release_branches:
              # Release branches are not feature branches.
              return False
          else:
              # Other valid branches are considered feature branches.
              return True