Consolidate documentation (#3071)

* 🔥 consolidate documentation
* ♻️ overwork std specializations
* 🚚 move images files to mkdocs
* ♻️ fix URLs
* 🔧 tweak MkDocs configuration
* 🔧 add namespaces
* 📝 document deprecations
* 📝 document documentation generation
* 🚸 improve search
* 🚸 add examples
* 🚧 start adding documentation for macros
* 📝 add note for https://github.com/nlohmann/json/issues/874#issuecomment-1001699139
* 📝 overwork example handling
* 📝 fix Markdown tables

doc/mkdocs/docs/api/basic_json/contains.md

@@ -1,12 +1,17 @@
-# basic_json::contains
+# <small>nlohmann::basic_json::</small>contains
 
 ```cpp
+// (1)
 template<typename KeyT>
 bool contains(KeyT && key) const;
+
+// (2)
+bool contains(const json_pointer& ptr) const;
 ```
 
-Check whether an element exists in a JSON object with key equivalent to `key`. If the element is not found or the JSON
-value is not an object, `#!cpp false` is returned.
+1. Check whether an element exists in a JSON object with key equivalent to `key`. If the element is not found or the 
+   JSON value is not an object, `#!cpp false` is returned.
+2. Check whether the given JSON pointer `ptr` can be resolved in the current JSON value.
 
 ## Template parameters
 
@@ -17,27 +22,45 @@ value is not an object, `#!cpp false` is returned.
 
 `key` (in)
 :   key value to check its existence.
-    
+
+`ptr` (in)
+:   JSON pointer to check its existence.
+
 ## Return value
 
-`#!cpp true` if an element with specified `key` exists. If no such element with such key is found or the JSON value is
-not an object, `#!cpp false` is returned.
+1. `#!cpp true` if an element with specified `key` exists. If no such element with such key is found or the JSON value
+   is not an object, `#!cpp false` is returned.
+2. `#!cpp true` if the JSON pointer can be resolved to a stored value, `#!cpp false` otherwise.
 
 ## Exception safety
 
 Strong exception safety: if an exception occurs, the original value stays intact.
 
+## Exceptions
+
+1. The function does not throw exceptions.
+2. The function can throw the following exceptions:
+    - Throws [`parse_error.106`](../../home/exceptions.md#jsonexceptionparse_error106) if an array index begins with
+      `0`.
+    - Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) if an array index was not a
+      number.
+
 ## Complexity
 
 Logarithmic in the size of the JSON object.
 
 ## Notes
 
-This method always returns `#!cpp false` when executed on a JSON type that is not an object.
+1. This method always returns `#!cpp false` when executed on a JSON type that is not an object.
+2. This method can be executed on any JSON value type.
 
-## Example
+!!! info "Postconditions"
 
-??? example
+    If `#!cpp j.contains(x)` returns `#!c true` for a key or JSON pointer `x`, then it is safe to call `j[x]`.
+
+## Examples
+
+??? example "Example (1) check with key"
 
     The example shows how `contains()` is used.
     
@@ -51,6 +74,21 @@ This method always returns `#!cpp false` when executed on a JSON type that is no
     --8<-- "examples/contains.output"
     ```
 
+??? example "Example (1) check with JSON pointer"
+
+    The example shows how `contains()` is used.
+    
+    ```cpp
+    --8<-- "examples/contains_json_pointer.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/contains_json_pointer.output"
+    ```
+
 ## Version history
 
-- Added in version 3.6.0.
+1. Added in version 3.6.0.
+2. Added in version 3.7.0.