title: escape metacharacters [ ] re2 in Google spreadsheets
body: <p>I want use the function <a href="https://support.google.com/docs/answer/3098244?hl=en" rel="nofollow">REGEXEXTRACT</a> in a Google spreadsheets for retrive a string between brackets.</p>
  
  <p>ex.
  in the cell A1 I have the text: <code>qwertyui (asdfghjk)</code><br>
  I need the text <code>asdfghjk</code>.</p>
  
  <p>The function <code>=REGEXEXTRACT(A1, "\(([A-Za-z /]+)\)")</code> works finely but when I have a text like <code>qwertyui ([asdfghjk])</code> the function doesn't return nothing because the regular expression that I use does not have the square brackets.</p>
  
  <p>I tried to add the characters "[" and "]" but they are metacharacters. I used the notation <code>\[</code> (and <code>\]</code>) but don't works.<br>
  Google spreadsheets use regular expression re2. Is the notation correct?</p>
  
  <p>Anyone know how to escape from metacharacters (or where I am wrong)?</p>