title: Evaluating strings using Regex
body: <p>I am using <code>Regex.IsMatch()</code> to evaluate a list of words. </p>
  
  <p>The <code>Regex</code> should return <code>true</code> if the following strings are evaluated:
  -hellotest
  -helloabc
  -abchello</p>
  
  <p>and the <code>Regex</code> should return false if the following strings are evaluated:
  -helloworld
  -worldtest
  -abcworld</p>
  
  <p>Basically I want it to return <code>true</code> if the word <code>"hello"</code> is found in the string and if the word <code>"world"</code> is <strong><em>not</em></strong> found in the string. </p>
  
  <p>What's the <code>Regex</code> to produce such result?</p>