Find Index in string with Regular Exprerssion starting with some index
<p>I want to search index of a string \n\n or \n \n or \n \s* \n  search start from some index like</p>

<pre><code> mystring.LastIndexof(regularexpression, mystartindex)
</code></pre>

<p>and similarly</p>

<pre><code>mystring.Indexof(regularexpression, mystartindex)
</code></pre>
