Clarify some things in 1.5.12

1-js/05-data-types/12-json/article.md

@@ -105,7 +105,7 @@ JSON is data-only language-independent specification, so some JavaScript-specifi
 Namely:
 
 - Function properties (methods).
-- Symbolic properties.
+- Symbolic keys and values.
 - Properties that store `undefined`.
 
 ```js run
@@ -276,6 +276,7 @@ name:         John
 name:         Alice
 place:        [object Object]
 number:       23
+occupiedBy: [object Object]
 */
 ```
 
@@ -328,6 +329,8 @@ alert(JSON.stringify(user, null, 2));
 */
 ```
 
+The third argument can also be a string. In this case, the string is used for indentation instead of a number of spaces.
+
 The `space` parameter is used solely for logging and nice-output purposes.
 
 ## Custom "toJSON"