@safe, pure and nothrow at the beginning of a module

[Philippe Sigaud via Digitalmars-d-learn]

In another module I marked as '@safe:' at the top, the compiler told
me that a class opEquals could not be @safe (because Object.opEquals
is @system).

So it seems that indeed a module-level '@safe:' affects everything,
since a class method was found lacking.

(I put a @trusted attribute on it).