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This is the shittiest of shit UX. Most web forum software is insecure and scales poorly and yet still does much better than that.
Using a domain specific language to enable powerful searches is a good idea, but it's a shit DSL. Google and Microsoft are just two examples where their web apps (Google Search, Gmail, Outlook OWA) offer this, but those all use reasonable and memorable terms. They don't expect us to remember how the relevant fields are named in the underlying database or code.
Pff, what's so hard about constructing your own search URL because some functionality isn't available in the GUI?