Importing a cropped area with FPDI

Question

I am creating a new PDF file by importing from an existing PDF, using FPDI.

$pdf->AddPage();
$pdf->setSourceFile("original.pdf");  
$tplIdx = $pdf->importPage(1);

How can I import a specific region from the existing PDF onto the new PDF that I am creating?

I have the variables, for example:

$x=5; //My desired box begins 5cm from the left
$y=4; // ...and 4cm from the top
$w=4; // ...and is 4cm wide
$h=5; // ...and 5cm in height

How can I import this specific area?