mod === obj    → true or false

Case Equality—Returns true if anObject is an instance of mod or one of mod’s descendents. Of limited use for modules, but can be used in case statements to classify objects by class.

Source Code

/*
*  call-seq:
*     mod === obj    => true or false
*  
*  Case Equality---Returns <code>true</code> if <i>anObject</i> is an
*  instance of <i>mod</i> or one of <i>mod</i>'s descendents. Of
*  limited use for modules, but can be used in <code>case</code>
*  statements to classify objects by class.
*/

static VALUE
rb_mod_eqq(mod, arg)
   VALUE mod, arg;
{
   return rb_obj_is_kind_of(arg, mod);
}