public static NestedArray::mergeDeep()
Merges multiple arrays, recursively, and returns the merged array.
This function is similar to PHP's array_merge_recursive() function, but it handles non-array values differently. When merging values that are not both arrays, the latter value replaces the former rather than merging with it.
Example:
$link_options_1 = array('fragment' => 'x', 'attributes' => array('title' => t('X'), 'class' => array('a', 'b')));
$link_options_2 = array('fragment