How can PHP developers effectively access and manipulate nested data within a JSON object?

To access and manipulate nested data within a JSON object in PHP, developers can decode the JSON string into an associative array using the `json_decode()` function. Once decoded, developers can access nested data using array notation or object notation depending on the structure of the JSON object. To manipulate nested data, developers can modify the values directly in the associative array and then encode the modified array back into a JSON string using the `json_encode()` function.

// JSON string containing nested data
$jsonString = '{"name": "John Doe", "age": 30, "address": {"street": "123 Main St", "city": "New York"}}';

// Decode JSON string into an associative array
$data = json_decode($jsonString, true);

// Access and manipulate nested data
$data['address']['city'] = 'Los Angeles';

// Encode modified array back into a JSON string
$modifiedJsonString = json_encode($data);

// Output modified JSON string
echo $modifiedJsonString;