mod < other   →  true, false, or nil

Returns true if mod is a subclass of other. Returns nil if there’s no relationship between the two. (Think of the relationship in terms of the class definition: "class A<B" implies "A<B").

Source Code

/*
* call-seq:
*   mod < other   =>  true, false, or nil
*
* Returns true if <i>mod</i> is a subclass of <i>other</i>. Returns 
* <code>nil</code> if there's no relationship between the two. 
* (Think of the relationship in terms of the class definition: 
* "class A<B" implies "A<B").
*
*/

static VALUE
rb_mod_lt(mod, arg)
   VALUE mod, arg;
{
   if (mod == arg) return Qfalse;
   return rb_class_inherited_p(mod, arg);
}