<p>How are callbacks written in PHP?</p>

Implementation of a callback is done like so
```
```
// This function uses a callback function. 
function doIt($callback) 
{ 
    $data = "this is my data";
    $callback($data); 
} 

// This is a sample callback function for doIt(). 
function myCallback($data) 
{ 
    print 'Data is: ' .  $data .  "\n"; 
} 

// Call doIt() and pass our sample callback function's name. 
doIt('myCallback');
```
```
Displays: Data is: this is my data