The examples presented for both ltrim() and rtrim() are accurate in their results, however the stated functions used is actually trim(). Thus, here are the corrected examples:
$string = " \n Hello World!"; echo ltrim($string);
echo ltrim($string, " \nA..Ha..z!"); // All capital letters between A and H, all lowercase letters, exclamation point, space, and newline
$string = "!Hello World42! \t\t"; echo rtrim($string);
echo rtrim($string, " \t!0..9"); // Range included is all numbers between 0 and 9, tab, space, and exclamation point.