Format for categories_string

[Guest]

Can someone help with the following line:

The original line reads

$categories_string .= '<a href="';

 

I need the correct way of inputting the line below (if its possible)

 

 

$categories_string .= '<a onmouseover="swapImage('hardware_3867');" onmouseout="reSwapImage('hardware_3867');" href="';