Shouldn't there be a way to only search multiple forums through some userscript? Only found out about userscript after messing around with an iOS app called HyperWeb.
At least in my limited understanding of userscript's capabilities, you'd still need to explicitly specify the forums you want to search, but I imagine that would solve lots of use cases for search filters.
Google has a limit to how long searches can be. So if it’s a complex one, it can’t be too long.
I think you can only specify searching one site at a time. With site: search filter.
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Google’s custom search engine’s where you can give a whitelisted amount of sites isn’t very good. At least not any more. It didn’t include lots of pages it’s main index does. Or the rankings were all out of sorts rendering not useful.
At least in my limited understanding of userscript's capabilities, you'd still need to explicitly specify the forums you want to search, but I imagine that would solve lots of use cases for search filters.