In Re: Checking the value of an undefined value, I wrote that the (new in Perl 5.10) "//" operator would do what the OP wanted. Afterward, I thought I'd written something like that before, so I swung over to Super Search to find it. I entered "//" for the text and "kyle" in the author box and hit search.
This seems to find most (but not all) of my nodes.
I found what I was looking for by searching for "5.10" (because I always point out that // is a 5.10 feature when I mention it), but I'm wondering why the original search (for "//") didn't work.
As I was writing this, I think I figured it out. It's finding the "//" in "[doc://defined]", for example.
I wonder if it would be worthwhile to have a checkbox to search for nodes "as rendered" rather than "as entered". I might even suggest making that the default, but that might be surprising to someone used to the old behavior.