set_allowed_types() in Upload library. Mistery?

[eluser]Ignacio[/eluser]
The function make an array with the values from $config['allowed_types'] to compare with the mimes array.

config here:

Code:

$config['allowed_types'] = 'gif|jpg|png';

the MAGIC function here:

Code:

function set_allowed_types($types)
{
    $this->allowed_types = explode('|', $types);
}

for here:

Code:

foreach ($this->allowed_types as $val)
{
    $mime = $this->mimes_types(strtolower($val));

    if (is_array($mime))
    {
        if (in_array($this->file_type, $mime, TRUE))
        {
            return TRUE;
        }
    }
    else
    {
        if ($mime == $this->file_type)
        {
            return TRUE;
        }    
    }        
}

I can't understand how set_allowed_types() is it working and not calling it anywhere.