title: C# Regular Expression to skip some special characters
body: <p>I am newbie to Regex and trying to learn that. My requirement is to ONLY consider a string as valid if it has JUST small alphabets, absolutely nothing else.
  ex: abc, khj, sdfs are valid words but Abc, KHJ,123,a$bd are not valid.</p>
  
  <p>I am writing a regular expression like this:   </p>
  
  <pre><code> private bool IsValid(string str)
   {
      Regex r = new Regex(@"[a-z][^&lt;&gt;%'=\$]");
      Console.WriteLine(str + " : " + r.IsMatch(str).ToString()); 
      return r.IsMatch(str);
   }
  </code></pre>
  
  <p>But when I pass on the following input to this method:</p>
  
  <pre><code>"a&lt;&gt;'b=b"
   "abc"
   "a$b"
  "123"
  "IHH"
  </code></pre>
  
  <p>it is identifying <code>abc</code> as valid but it is also recognizing <code>a$b</code> and <code>a&lt;&gt;'b=b</code> as valid words ! (returning <code>true</code> for those)
  I want to understand how to skip <code>a$b</code> and <code>a&lt;&gt;'b=b ??</code> the method should return <code>false</code> for them.</p>
  
  <p>Please help me understand. </p>
  
  <p>Thanks</p>