Rollup merge of #30428 - steveklabnik:quickfix, r=apasel422

Author: steveklabnik

src/libstd/primitive_docs.rs

@@ -333,7 +333,7 @@ mod prim_slice { }
 /// let ptr = story.as_ptr();
 /// let len = story.len();
 ///
-/// // story has thirteen bytes
+/// // story has nineteen bytes
 /// assert_eq!(19, len);
 ///
 /// // We can re-build a str out of ptr and len. This is all unsafe becuase