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php preg regex - group of whitspaces without linebreak in multiline mode
preg_match_all("/^s*+(.+)[^$s]*+$/m", $_POST['input'], $matches, PREG_SET_ORDER );

$lines = array_map("trim", explode("n", $_POST["input"]));
 // quite a handy utility function, so just wanted to note that here

preg_split('/((?!n)p{Z})*n((?!n)p{Z})*/u', "...n...");

preg_match_all("/s*(.*S)/", $_POST['input'], $matches, PREG_SET_ORDER );