title: What does the skiplistnode variable "span" mean in redis.h?
body: <p>In <code>redis.h</code>, the skipnode is defined as below:</p>
  
  <pre><code>typedef struct zskiplistNode {
      robj *obj;
      double score;
      struct zskiplistNode *backward;
      struct zskiplistLevel {
          struct zskiplistNode *forward;
          unsigned int span;
      } level[];
  } zskiplistNode;
  </code></pre>
  
  <p>What does the var <code>span</code> mean? What does this var store?</p>