Checklist p. 246 class func?


I am confused with the following code:

  class func nextChecklistItemID() -> Int {

        let userDefaults = NSUserDefaults.standardUserDefaults()
        let itemID = userDefaults.integerForKey("ChecklistItemID")
        userDefaults.setInteger(itemID + 1, forKey: "ChecklistItemID")
        return itemID

why should it be class func, instead of just func?

I am afraid I do not understand a basic concept of something…


sorry, I should have read a little bit more before having rushed to ask.