Updated FAQ (markdown)

FAQ.md

@@ -2,6 +2,31 @@
 
 See [Compatibility issues](Compatibility issues) first.
 
+### Should I call `parseArray()` or `parseObject()`?
+
+This is a very common question as people are often confused when the JSON input contains mixed arrays and objects.
+
+The answer is very simple: it's the type of the root that matters.
+This means that you just need to look at the first character: it's either a `[`, for an array, or a `{`, for an object.
+
+For example, if the input is:
+
+```json
+{"mickey":["mouse"],"donald":["duck"]}
+```
+
+then you must call `parseObject()` because the root is an object.
+
+And, if the input is:
+
+```json
+[{"mickey":"mouse","donald":"duck"}]
+```
+
+then you must call `parseArray()` because the root is an array.
+
+Finally, if you cannot know in advance the type of the root, please open an issue. Don't worry this can be implemented very easily, it's just that nobody asked for it.
+
 ### Why parsing fails?
 
 The parsing functions, `parseArray()` and `parseObject()`, may fail for 3 reasons: