VS2013 can't replace content with $1, why?
<p>I am using VS2013, and i want replace some text. Because the file has many alike word， so i have to use regex look ahead, look behind so search and replace.</p>

<p>text.txt:</p>

<pre><code>abc adc
</code></pre>

<p>regex: </p>

<pre><code>(?&lt;=a)([a-z])(?=c)
</code></pre>

<p>and replace with </p>

<pre><code>xxx$1xxx
</code></pre>

<p>But failed to replace all, Anyone konw this why?</p>