title: Extract all substrings beginning and ending with a regex from large string
body: <p>I have a large string which contains multiline-substrings between two constant marker-strings, which I can identify with a regex.</p>
  
  <p>For simplification I named them <code>abcdef</code> and <code>fedcba</code> here:</p>
  
  <pre><code>abcdef Sed lobortis nisl sed malesuada bibendum. fedcba
  ...
  
  abcdef Fusce odio turpis, accumsan non posuere placerat. 
  1
  2
  3
  fedcba
  
  abcdef Aliquam erat volutpat. Proin ultrices fedcba
  </code></pre>
  
  <p>How can I get all the occurrences <em>including</em> the markers from the large string?</p>