To merge an array of strings into a single string split by a new line in PHP, you can use the `implode` function to join the array elements into a single string, with the new line character (`\n`) as the delimiter.
Here's an example code snippet:
// An array of strings
$array_of_strings = array('Hello', 'world', 'in', 'PHP');
// Merge the array into a single string with new line delimiter
$merged_string = implode("\n", $array_of_strings);
// Output the merged string