title: Outlook contextual addin can't find PLUS sign with regex
body: <p>My rule looks like this</p>
  
  <pre><code>&lt;ExtensionPoint xsi:type="DetectedEntity"&gt;
    &lt;Label resid="contextLabel" /&gt;
    &lt;SourceLocation resid="testResId" /&gt;
    &lt;Rule xsi:type="RuleCollection" Mode="And"&gt;
      &lt;Rule xsi:type="RuleCollection" Mode="Or"&gt;
        &lt;Rule xsi:type="ItemIs" ItemType="Message" /&gt;
        &lt;Rule xsi:type="ItemIs" ItemType="Appointment" /&gt;
      &lt;/Rule&gt;
      &lt;Rule xsi:type="ItemHasRegularExpressionMatch" RegExName="Test" RegExValue="\+1" PropertyName="BodyAsPlaintext" Highlight="All"/&gt;
    &lt;/Rule&gt;
  &lt;/ExtensionPoint&gt;
  </code></pre>
  
  <p>as you can see the regex is looking for a <code>+1</code> to highlight (my real regex does more than that, but this example is enough to reproduce the issue)</p>
  
  <p>It seems like the search works, since it returns the results, but i see errors in the dev console and highlight is not happening.
  My guess is Outlook is using the actual matches to highlight and put them into a new regex (which in fact cannot start with a plus sign).
  The exception is:</p>
  
  <pre><code>constants.ts:1 Uncaught (in promise) SyntaxError: Invalid regular expression: /+1/: Nothing to repeat
      at new RegExp (&lt;anonymous&gt;)
      at constants.ts:1
      at Array.forEach (&lt;anonymous&gt;)
      at markElements.ts:54
      at AAQkADAzYTZlYTYyLWQyMGMtNDFhOS05MTAzLTQyYjJhNjBhMTYwZgAQAINoPf%2BPCdhNj6AVUpiXz4w%3D:347
      at Object.next (AAQkADAzYTZlYTYyLWQyMGMtNDFhOS05MTAzLTQyYjJhNjBhMTYwZgAQAINoPf%2BPCdhNj6AVUpiXz4w%3D:347)
      at a (AAQkADAzYTZlYTYyLWQyMGMtNDFhOS05MTAzLTQyYjJhNjBhMTYwZgAQAINoPf%2BPCdhNj6AVUpiXz4w%3D:347)
  </code></pre>
  
  <p>I did not find any documentation on the office addin development sites if/how should i escape these. Any idea?</p>