title: Regular expression that matches string equals to one in a group
body: <p>E.g. I want to match string with the same word at the end as at the begin, so that following strings match:</p>
  
  <pre><code>aaa dsfj gjroo gnfsdj riier aaa
  sdf foiqjf skdfjqei  adf sdf sdjfei sdf
  rew123 jefqeoi03945  jq984rjfa;p94  ajefoj384 rew123
  </code></pre>