Should I use “in” or “on”?
What is the difference between these two phrases? Which is more common?
find something in the wiki
find something on the wiki
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I lean towards in the wiki, but I think that is simply because the usage is more common and has become idiomatic. Whether we look "in" or "on" a reference derives from our actions towards its physical incarnation, thus
However, when referring to a specific wiki, I would use on. A wiki is a type of website, and websites are almost invariably "on":
It is in the wiki.
Wiki is a community edited knowledge base, in which one could find something.