Searches for unfamiliar special characters should work. Single-character operators and syntactic sugar are one of the harder things to google for, and consequently, a big advantage of a purpose made language reference tool like you've made.

A simple solution:

    ?   -> Optionals
    ??  -> nil coalescing
    !   -> Implicitly Unwrapped Optionals
    <>  -> Generics
    as? -> type casting

…and so on

A Better solution:

provide a wikipedia-like disambiguation section for special characters (since `!` could be Implicitly unwrapped optionals, Forced unwrapping, or boolean negation)