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For example, if you're looking for a trade shop with say, a Ditto, you could search Ditto, check the box if it's not in any titles, and search this forum only.
Lady SalamenceUnowninator I am messing around with the advanced options in the search bar and no, there is not yet a feature for this. As for your purposes for Wi-Fi, a simple search for "Ditto" in the wi-fi forum will usually lead to a thread with a Ditto in the OP. I say this because most instances of "Ditto" will be "CMT for your Ditto x/31/31/31/31/0" or things of that nature, in which case you can just go to the OP of that thread to verify that there indeed is a Ditto.
This is a flimsy solution to a legitimate problem though, and is obviously not applicable to any other forum on the site. I'll talk to some of the programmers to see if this is possible.
I am not completely sure if this does the same thing but I carried a search for Ditto in the Wi-Fi forum with "Search this forum only" and "Display results as threads". What I think that search does is search for Ditto in every thread and just display them as thread. HOWEVER, by displaying results as threads, if the results have the Ditto word bolded then that I think means that the first post of that thread has Ditto in it. Anything else that shows up as results do not have Ditto in the result probably has Ditto found in some other part of the thread but not in the OP.
This is probably the easiest way to tell whether the search can be found in the first post of the thread without opening up threads and using ctrl+f.
Also from some casual searching on Google I don't think there's currently a search add-on for xenforo that allows searching for first post only.