docs: def is_clean(self):
          """
          :data:`True` if the working tree (and index) is clean, :data:`False` otherwise.
  
          The implementation of :attr:`GitRepo.is_clean` checks whether ``git
          diff`` reports any differences. This command has several variants:
  
          1. ``git diff`` shows the difference between the index and working tree.
          2. ``git diff --cached`` shows the difference between the last commit and index.
          3. ``git diff HEAD`` shows the difference between the last commit and working tree.
  
          The implementation of :attr:`GitRepo.is_clean` uses the third command
          (``git diff HEAD``) in an attempt to hide the existence of git's index
          from callers that are trying to write code that works with Git and
          Mercurial using the same Python API.
          """
          # Make sure the local repository exists.
          self.create()
          # Check whether the `git diff HEAD' output is empty.
          listing = self.context.capture('git', 'diff', 'HEAD', check=False, silent=True)
          return len(listing.splitlines()) == 0