title: Case-insensitive regex to change html <br> tag
body: <p>My requirement is to change all <code>&lt;br /&gt;</code> tags to <code>&lt;br&gt;</code> in a string. <code>&lt;Br /&gt;</code>, <code>&lt;bR /&gt;</code>, <code>&lt;BR /&gt;</code>, <code>&lt;br /&gt;</code> all four combination in a string should be changed into <code>&lt;br&gt;</code>. </p>
  
  <p>How to write a regex for this in C#?</p>
  
  <p>Converting string into uppercase or lowercase is not allowed.</p>