title: Explain for(var cat in livingCats) syntax?
body: <pre><code>livingCats = {"bob": true, "bo": false};
  for(var cat in livingCats)
    print(cat);
  </code></pre>
  
  <p>This outputs all of  the names in the object whether it is true or not. 
  I do not remember defining cat as anything in the object, so why can we use cat to print each name?
  Can cat be exchanged for anything and it does not matter?</p>
  
  <p>More info please on the syntax of using a var and in to print the keys.</p>
  
  <p>from the answers and from reading more into the documentation that the cat variable was not defined but is an enumerable, thus can be used in for..in. Cat can be replaced by anything.</p>