Actually now that I do more searching (Cmd-f) in Preview, I have to admit I cannot tell exactly what it is doing. Explicit quoting doesn't work for phrases, but it is definitely doing more than an "OR" search if you give them without quotes. In any case, if this is something outside the scope of the API you have access to, I guess there's not much you can do. Knowing Apple, they probably use some entirely different private API for their own internal applications. I'd be happy to report a bug to Apple,...
Phrase search misses line-broken results (1.7.4)