Hàm trim() trong PHP - PHP Function

$text   = "           ------This is a test -- string :) ...     ";
$hello  = "Hello World";
var_dump($text);
echo "<br />";
var_dump($hello);
echo "<br />";

$trimmed = trim($text);
var_dump($trimmed);
echo "<br />";

$trimmed = trim($text, " -.");
var_dump($trimmed);
echo "<br />";

$trimmed = trim($hello, "Hdle");
var_dump($trimmed);
echo "<br />";

$trimmed = trim($hello, 'HdWr');
var_dump($trimmed);
echo "<br />";

string(53) " ------This is a test -- string :) ... " 
string(11) "Hello World" 
string(37) "------This is a test -- string :) ..." 
string(27) "This is a test -- string :)" 
string(5) "o Wor" 
string(9) "ello Worl"