Why adding "nf=1" to iframe?

[Cameron]

There is such line in "wawp.php":
$attrs['src'] = complete_url($attrs['src']) .
'&nf=1';

I don't know why "nf=1" is added. And why don't we need to check
whether "?" exists.

An error will trigger in English version of Google. There is an iframe
with src="" in index of Google. WAWP will replace "" with "&nf=1"
which make it attempt to access "http://www.google.com/&nf=1". This
trigger an network error.

This error can be captured by Firebug.

Regrads.
Cameron