448     fn add(mut self, rhs: &'a str) -> Self::Output {  in add()
449         self += rhs;  in add()
460     fn add(mut self, rhs: Cow<'a, str>) -> Self::Output {  in add()
461         self += rhs;  in add()
469     fn add_assign(&mut self, rhs: &'a str) {  in add_assign()
471             *self = Cow::Borrowed(rhs)  in add_assign()
472         } else if !rhs.is_empty() {  in add_assign()
474                 let mut s = String::with_capacity(lhs.len() + rhs.len());  in add_assign()
478             self.to_mut().push_str(rhs);  in add_assign()
486     fn add_assign(&mut self, rhs: Cow<'a, str>) {  in add_assign()
488             *self = rhs  in add_assign()
489         } else if !rhs.is_empty() {  in add_assign()
491                 let mut s = String::with_capacity(lhs.len() + rhs.len());  in add_assign()
495             self.to_mut().push_str(&rhs);  in add_assign()