To access a class method from an instance, you have to use the reference to that class (because that’s where the method resides). The attribute reader that returns that reference is named class
If you come from another language, you might be tempted to use the += operator when appending to a string.
Sometimes, you want to initialize a variable to some value only if that variable is equal to nil. If you like to write your methods as short, clean and readable as possible, you can do that task in a single line instead of taking the traditionnal 3 lines approach.