title: How to efficiently insert elements after another known (by key or pointer) element in a PHP array?
body: <p>Given an array:</p>
  
  <pre><code>$a = array(
      'abc',
      123,
      'k1'=&gt;'v1',
      'k2'=&gt;'v2',
      78,
      'tt',
      'k3'=&gt;'v3'
  );
  </code></pre>
  
  <p>With its internal pointer on one of its elements, how do I insert an element after the current element?
  And how do I insert an element after a key-known element, say 'k1'?</p>
  
  <p>Performance Care~</p>