Question about "nofollow"

I'm working on a service that returns strictly dofollow results, hence I'm trying to detect a specific way to find nofollow websites and void them? What are the exact strings I should be looking for?

rel="nofollow
rel=nofollow
, nofollow">
, nofollow>

Code (markup):

Would these hold up?

 

There are a number of variations and even coding mistakes. You are better off just searching for nofollow.

 

I then risk the chance of voiding tons of SEO-related sites that discuss nofollow.

 

you do not search for nofollow on the site content but on the page source.

 

The site's content will be in the source...

 

thats true but you dont look for the content in the source. you look for external link nofollow in the source. its easy to distinguish the two. when you see rel="nofollow", you know its enternal nofollow but you dont have to search with rel="nofollow", you can just search for nofollow to make your life easy. as long as you know what to look for

 

Yes.. this is the only way to know about nofollow..

 

nofollow is useless for SEO point of view, it permits crawler to follow or donot follow the link. The only way to find nofollow attribute is just see the source code and find the nofollow tag in that.