title: Odd behaviour when using word boundaries [[:<:]] and [[:>]]
body: <p>My task is to create a blacklist for entries in different strings. I am checking for the entries right in database using <code>MySQL</code>. </p>
  
  <p>You probably know about word boundary marks in <code>MySQL</code>:
  <code>[[:&lt;:]]</code> and <code>[[:&gt;:]]</code> which correspond to <code>\b</code> in default regexps.</p>
  
  <p>Something goes wrong when there are <code>regexp special characters</code> and <code>word boundary marks</code> in a string. </p>
  
  <p><strong>But those characters are escaped by double backslashes!</strong></p>
  
  <p>Just run this query</p>
  
  <pre><code>SELECT 
  "test()" REGEXP "[[:&lt;:]]test\\(\\)[[:&gt;:]]", 
  "test()" REGEXP "test\\(\\)", 
  "test"   REGEXP "[[:&lt;:]]test[[:&gt;:]]",
  "test"   REGEXP "test" ;
  </code></pre>
  
  <p>And you will get </p>
  
  <pre><code>0 | 1 | 1 | 1
  </code></pre>
  
  <p>Instead of expected</p>
  
  <pre><code>1 | 1 | 1 | 1
  </code></pre>
  
  <p>Could someone, please, explain how to solve the issue?</p>