Ask HN: Tool to detect what user searches on your webpage

Is there a tool which detects what people are searching on your webpage? Do you think it could be useful? what for? Other than finding possible hyperlinks Can you get the info from the browser? I know you could hijack ctrl f but I hate when sites are doing it. You could side channel based on the jumping in the location in the page I guess. I have no use for it and not creating dom scripts, but I think some people would find it useful I think it would be an interesting challenge for someone here Thanks