docs: function isBuiltIn(obj) {
  
  	// If primitive, array, or POJO return true. Also check if
  	// it is not a POJO but is some type like [object Date] or
  	// [object Regex] and return true.
  	if (isPrimitive(obj) ||
  		Array.isArray(obj) ||
  		isPlainObject(obj) ||
  		(Object.prototype.toString.call(obj) !== '[object Object]' &&
  			Object.prototype.toString.call(obj).indexOf('[object ') !== -1)) {
  		return true;
  	}
  	else {
  		return false;
  	}
  }