Google searches everywhere, pretty much, and the search within a particular website is often rubbish. Often seriously rubbish. But you can combine the two to get straight to what you want.
For example, if you wanted to find every mention of OmniFocus on this site, The Blank Screen, then you would need hours of reading but practically no time searching. Just go to Google and type”
OmniFocus at williamgallagher.com
That’s it. Google will now search williamgallagher.com for the word OmniFocus. The search page will go on and tell you more from other places, especially if anyone’s linked to my blathering on about that To Do software, but the top results will be the ones you want on the site you’re searching.