nerdfisch: DevBits

$form['nodes'] = [
    '#title' => $this->t('Select articles'),
    '#type' => 'entity_autocomplete',
    '#target_type' => 'node',
    '#tags' => TRUE,
    '#selection_handler' => 'default',
    '#selection_settings' => ['target_bundles' => ['article']],
    '#default_value' => $default_nodes,
];

$form['nodes'] = [
    '#title' => $this->t('Select articles'),
    '#type' => 'entity_autocomplete',
    '#target_type' => 'node',
    '#maxlength' => 1024,
    '#tags' => TRUE,
    '#selection_handler' => 'default',
    '#selection_settings' => ['target_bundles' => ['article']],
    '#default_value' => $default_nodes,
];

// Default, only plaintext.
xdebug.cli_color=0
// Coloured if your terminal will support it.
xdebug.cli_color=1
// Forced coloured output.
xdebug.cli_color=2

/* Views exposed filter: appropriate field widths */
.views-exposed-form #edit-nid {
  max-width: 10ch;
}

use Drupal\Component\Utility\NestedArray;

// Parent array with default settings.
$parent_array = [
    'config' => [
        'theme' => 'dark',
        'layout' => [
            'width' => 800,
            'height' => 600,
        ],
    ],
];

// Child array adds more nested data but doesn't override existing values.
$child_array = [
    'config' => [
        'layout' => [
            'depth' => 300, // New nested key
        ],
        'features' => [
            'animations' => true, // New section
        ],
    ],
];

// Merge both arrays.
$merged_array = NestedArray::mergeDeep($parent_array, $child_array);

[
    'config' => [
        // Unchanged (not overridden)
        'theme' => 'dark', 
        'layout' => [
            // Keeps parent value
            'width' => 800, 
            // Keeps parent value  
            'height' => 600,
            // New nested key added
            'depth' => 300,   
        ],
        'features' => [
            // New section added
            'animations' => true, 
        ],
    ],
]