code: def all(self):
          r
          for arg in self.args:
              for expr in arg:
                  yield expr
          for content in self._contents:
              yield content
docs: r"""Returns all content in this expression, regardless of whitespace or
          not. This includes all LaTeX needed to reconstruct the original source.
  
          >>> expr1 = TexExpr('textbf', ('\n', 'hi'))
          >>> expr2 = TexExpr('textbf', ('\n', 'hi'), preserve_whitespace=True)
          >>> list(expr1.all) == list(expr2.all)
          True