You can add short documentation strings to your classes, methods, data members and functions by placing them in quotes inside the declaration, like so:

class Example "An example class" {
    var string some_string "An example data member";
    function some_method() : int "An example method";
}
function some_function() "An example global function";

These are made available to the S2 backend support code, and applications may provide some kind of documentation browsing facility or the ability to generate static files containing documentation.