title: what are the properties of a variable in objective-c that is declared above @interface in a *.h file? (sample attached)
body: <p>I saw the following in some code (see below). Have not come across the concept of a variable being declared above the @interface.   What is the concept here? / What are the properties of this variable and how it could be used?</p>
  
  <pre><code>#import &lt;Foundation/Foundation.h&gt;
  
  NSMutableArray* testArray;  // &lt;=== HERE
  
  @interface MyClass : NSObject {
  }
  @end
  </code></pre>