title: Invalid escape sequence in literal with regex
body: <p>I define a string with:</p>
  
  <pre><code>static let Regex_studio_tel = "^(0[0-9]{2,3}\-)?([2-9][0-9]{6,7})+(\-[0-9]{1,4})?$"
  </code></pre>
  
  <p>But there comes an issue:</p>
  
  <blockquote>
    <p>Invalid escape sequence in literal </p>
  </blockquote>
  
  <p>The picture I token:</p>
  
  <p><a href="https://i.stack.imgur.com/pcJx6.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/pcJx6.jpg" alt="enter image description here"></a></p>
  
  <hr>
  
  <p><strong>Edit -1</strong></p>
  
  <p>My requirement is match special plane numbers use Regex, such as:</p>
  
  <p>My company have a special plane number： </p>
  
  <pre><code>028-65636688 or 85317778-8007  
  </code></pre>
  
  <p>// <code>aaa-bbbbbbbb-ccc</code> we know the <code>aaa</code> is the prefix, and it means City Dialing Code， and <code>bbbbbbbb</code> is the main tel number, <code>cccc</code> is the landline telephone's extension number,</p>
  
  <p>such as my company's landline telephone is <code>028-65636688</code>, maybe our company have 10 extension number: <code>028-65636688-8007 ,028-65636688-8006,028-65636688-8005</code> and so on.
  Of course, it maybe have a ext-number at the end. </p>
  
  <pre><code>028-65636688-2559
  </code></pre>