[Fizzlemizz]

So, not an event but a frame method (function)

function frame:SomeFunc(arg1, arg2)
    self:SetAlpha(arg1)
    if arg2 == "something" then
        -- do other stuff
    end
end

frame:SomeFunc(0.5, "something")

You can also use a Mixin to apply methods but that ends up being the same thing.