// Extract a substring from the start of the string $str = "Hello, world!"; echo substr($str, 0, 5); // Output: Hello // Extract a substring from the middle of the string $str = "The quick brown fox jumps over the lazy dog"; echo substr($str, 16, 9); // Output: brown fox // Extract a substring from the end of the string $str = "1234567890"; echo substr($str, -3); // Output: 890Based on the function name and parameter usage, it is likely that this function is part of the standard PHP library for manipulating strings. Therefore, it would not be part of an external package library.