M477HEW

I'm really new to PHP and am currently using the framework of an existing site to help me learn the ropes. I have the following line of code and I'm kind of stuck. I'm OK up to the ['long_descr'] but after that I am lost. Can anyone help me out and explain this line of code to me please? I'm particularly confused by the last half - ,0,20 etc. What do these numbers represent? $index=strpos(substr($data[0]['long_descr'],0,20),'same_as'); Thanks in advance for any help Matt