So far, in this book, we have been using Puppet's built-in facts, such as the ipaddress_eth1 and uptime. In comparison to functions, facts are much easier to use as they don't accept arguments. We just reference them like we reference any Puppet variable using the $fact_name or $::fact_name syntax. Personally, I like to use the $::fact_name syntax because it clearly defines the scope of the variable. This is also the syntax recommended in the Puppet Language Style Guide (https://docs.puppetlabs.com/guides/style_guide.html). The $:: prefix in Puppet variables means that the variable scope is global ($::fact_name) as opposed to local ($fact_name). Although Puppet doesn't allow you to declare a local variable with the same name as a fact, it is a good practice to include the scope prefix ($::) when referencing facts. When someone is studying a manifest that I've written, they can easily see from the $:: prefix that the variable is referencing the fact rather than the local...