code: function isAssignableFrom(ctor, toTest) {
  
    if (!(ctor instanceof Function) || !(toTest instanceof Function)) {
      throw new Error('arguments must be Functions.');
    }
  
    if (ctor === Object || ctor === toTest) {
      return true;
    }
  
    if (toTest.super_) {
      return isAssignableFrom(ctor, toTest.super_);
    }
  
    return false;
  }
docs: @private
  
  @description
  
  Returns `true` if the first constructor function is equal to, or a super of,
  the second constructor function.
  
  @param {Function} ctor the constructor function that might be equal to or a super of 'toTest'.
  @param {Object} toTest the constructor function to test