title: How to replace some part of the text using regex c#
body: <p>for example:</p>
  
  <pre><code>string str = $@"&lt;html&gt; &lt; head &gt; &lt;/ head &gt; &lt; body &gt; &lt;start&gt; &lt; h1 &gt; Header 1 &lt;/ h1 &gt; &lt; p &gt; A worker can be of 3 different types.&lt;/ p &gt; &lt;end&gt; &lt; p &gt;&lt;/ p &gt; &lt;/ body &gt; &lt;/ html &gt; "
  string replacement = "hello world";
  string newString = $@"&lt;html&gt; &lt; head &gt; &lt;/ head &gt; &lt; body &gt; &lt;start&gt; &lt; h1 &gt; Header 1 &lt;/ h1 &gt; &lt; p &gt; hello world&lt;/ p &gt; &lt;end&gt; &lt; p &gt;&lt;/ p &gt; &lt;/ body &gt; &lt;/ html &gt; "
  </code></pre>
  
  <p>So I have a <code>&lt;start&gt;</code> and <code>&lt;end&gt;</code> sign to know which part of the text should be replaced. How I can get the <code>newString</code> by regex.</p>