deploy: 63c10a51fc

features/element_access/index.md

@@ -5,5 +5,17 @@ There are many ways elements in a JSON value can be accessed:
 - unchecked access via [`operator[]`](https://json.nlohmann.me/features/element_access/unchecked_access/index.md)
 - checked access via [`at`](https://json.nlohmann.me/features/element_access/checked_access/index.md)
 - access with default value via [`value`](https://json.nlohmann.me/features/element_access/default_value/index.md)
-- iterators
-- JSON pointers
+- [iterators](https://json.nlohmann.me/features/iterators/index.md)
+- [JSON pointers](https://json.nlohmann.me/features/json_pointer/index.md)
+
+Testing whether a key or index exists before accessing it is also possible, with [`contains`](https://json.nlohmann.me/api/basic_json/contains/index.md) or [`find`](https://json.nlohmann.me/api/basic_json/find/index.md) (which returns an iterator to the value, or `end()` if it is not found).
+
+```
+flowchart TD
+    A["accessing a value"] --> B{"must it exist?"}
+    B -->|"yes, missing is an error"| C["at() -- throws"]
+    B -->|"yes, but checking is my job"| D["operator[] -- unchecked"]
+    B -->|"no, a fallback is fine"| E["value() -- default value"]
+    A --> F{"just testing first?"}
+    F -->|"yes"| G["contains() / find()"]
+```