docs: function one_space(left, right) {
          left = left || token;
          right = right || next_token;
          if (right.id !== '(end)' && !option.white &&
                  (token.line !== right.line ||
                  token.thru + 1 !== right.from)) {
              warn('expected_space_a_b', right, artifact(token), artifact(right));
          }
      }