title: invalid escape in pattern HTML/Javascript
body: <p>I am trying to make an <code>&lt;input&gt;</code> field that uses a pattern to check if the input is a valid windows file path.</p>
  
  <p>The pattern I have is</p>
  
  <pre><code>/^(?:[\w]\:|\\)(\\[a-zA-Z_\-\s0-9\.()~!@#$%^&amp;=+';,{}\[\]]+)+\.(exe)$/g
  </code></pre>
  
  <p>However, when putting this into the pattern attribute of an <code>&lt;input&gt;</code> field:</p>
  
  <pre><code>&lt;input id="path" type="text" pattern="^(?:[\w]\:|\)(\[a-zA-Z_\-\s0-9\.()~!@#$%^&amp;=+';,{}[]]+)+\.(exe)$"&gt;
  </code></pre>
  
  <p>An error is displayed in the console saying:</p>
  
  <pre><code>Pattern attribute value
  ^(?:[\w]\:|\\)(\\[a-zA-Z_\-\s0-9\.()~!@#$%^&amp;=+';,{}\[\]]+)+\.(exe)$ is
  not a valid regular expression:  Uncaught SyntaxError: Invalid regular
  expression: /^(?:[\w]\:|\\)(\\[a-zA-Z_\-\s0-9\.()~!@#$%^&amp;=+';,{}\[\]]+)+\.(exe)$/:
  Invalid escape
  </code></pre>
  
  <p>I have tried several ways of writing this pattern, but none seem to work.</p>